Ilt3 ligand

ABSTRACT

The present invention provides antibodies and antigen-binding fragments thereof that bind ILT3, ILT3 ligand (i.e., PI16) or a complex between ILT3 and the ILT3 ligand. Methods for determining whether ILT3 and the ILT3 ligand bind together or whether a substance agonizes or antagonizes such binding are also provided.

BACKGROUND OF THE INVENTION (1) Field of the Invention

The present invention relates to ILT3 and an ILT3 ligand as well as antibodies that bind thereto and methods related thereto. In a specific embodiment the ILT3 ligand is peptidase inhibitor 16 (PI16).

(2) Description of Related Art

Peptidase inhibitor 16 (PI16) is also known as CRISP-9 (cysteine-rich secretory protein 9) or Prostrate Secretory Protein Binding Protein(PSPBP; binds prostate secretory protein 94 (PSP94)). PI16 belongs to cysteine-rich secretory proteins, antigen 5, and pathogenesis-related 1 proteins (CAP) family. Members of this family includes human glioma pathogenesis-related 1 (GLIPR1), Golgi associated pathogenesis related-1 protein (GAPR1), and mannose receptor like and R3H domain containing proteins. PI16 is often found secreted, may have endocrine or paracrine function, or involvement in ECM regulation and branching morphogenesis. The CAP superfamily is suggested to have roles in reproduction, cancer, and immune defense (Gibbs et al., Endocr Rev 29:865-897 (2008)).

ILT3 (Immunoglobulin-like transcript 3), also known as CD85k or LIR-5, is an approximately 60 kDa transmembrane glycoprotein that negatively regulates immune cell activation. Mature human ILT3 has a 238 amino acid extracellular domain with two Ig-like domains, a 21 amino acid transmembrane segment, and a 168 amino acid cytoplasmic domain with 3 immunoreceptor tyrosine-based inhibitory motifs (ITIM). Alternative splicing of human ILT3 generates an isoform that lacks the first ITIM and a secreted isoform that circulates in the serum of cancer patients. ILT3 is expressed on dendritic cells (DCs), monocytes, macrophages, and vascular endothelial cells (ECs). Ligation of ILT3 triggers ITIM-mediated inhibition of cell-activating signaling, leading to enhanced immune tolerance and reduced allogeneic graft rejection. Soluble ILT3 induces the differentiation of CD8 T suppressor cells (Ts) that can inhibit the effector functions of CD4+ Th cells and CD8+ CTL. In turn, CD8 Ts cells induce ILT3 up-regulation and a tolerogenic phenotype in monocytes, DCs, and ECs.

Recently, Intl. Pub. No. WO2017015227 reported that CD166, also known as lymphocyte cell adhesion molecule (ALCAM), was a ligand for ILT3 and provides methods for treating cancer comprising in some embodiments an antibody against CD166 or ALCAM.

SUMMARY OF THE INVENTION

The inventors have identified PI16 as a ligand for ILT3 and provides herein antibodies that bind ILT3 in a complex with PI16. Thus, the present invention provides an antibody or antigen-binding fragment that binds to a complex between ILT3 and the ILT3 ligand PI16, which in particular embodiments, does not bind to ILT3 or ILT3 ligand when not in said complex. The present invention also provides a multispecific (e.g., bispecific) antibody or antigen-binding fragment thereof that specifically binds to ILT3 and ILT3 ligand PI16. The present invention further provides a composition comprising an antibody or antigen-binding fragment thereof that specifically binds to ILT3 and an antibody or antigen-binding fragment thereof that specifically binds to ILT3 ligand PI16.

The present invention provides an antibody or antigen-binding fragment that specifically binds to an complex between ILT3 and ILT3 ligand (e.g., PI16) but does not bind to ILT3 or ILT3 ligand which are not in said complex. In an embodiment of the invention, the antibody or antigen-binding fragment thereof comprises a heavy chain variable region comprising: CDR1 comprising the amino acid sequence of SEQ ID NO:10; CDR2 comprising the amino acid sequence of SEQ ID NO:11; CDR3 comprising the amino acid sequence of SEQ ID NO:12; and a light chain variable region comprising: CDR1 comprising the amino acid sequence of SEQ ID NO:13; CDR2 comprising the amino acid sequence of SEQ ID NO:14; CDR3 comprising the amino acid sequence of SEQ ID NO:15; or a heavy chain variable region comprising: CDR1 comprising the amino acid sequence of SEQ ID NO:18; CDR2 comprising the amino acid sequence of SEQ ID NO:19; CDR3 comprising the amino acid sequence of SEQ ID NO:20; and a light chain variable region comprising: CDR1 comprising the amino acid sequence of SEQ ID NO 21; CDR2 comprising the amino acid sequence of SEQ ID NO:22; CDR3 comprising the amino acid sequence of SEQ ID NO:23; or a heavy chain variable region comprising: CDR1 comprising the amino acid sequence of SEQ ID NO:26; CDR2 comprising the amino acid sequence of SEQ ID NO:27; CDR3 comprising the amino acid sequence of SEQ ID NO:28; and a light chain variable region comprising: CDR1 comprising the amino acid sequence of SEQ ID NO:29; CDR2 comprising the amino acid sequence of SEQ ID NO:30; CDR3 comprising the amino acid sequence of SEQ ID NO:31; or a heavy chain variable region comprising: CDR1 comprising the amino acid sequence of SEQ ID NO:34; CDR2 comprising the amino acid sequence of SEQ ID NO:35; CDR3 comprising the amino acid sequence of SEQ ID NO:36; and a light chain variable region comprising: CDR1 comprising the amino acid sequence of SEQ ID NO:37; CDR2 comprising the amino acid sequence of SEQ ID NO:38; CDR3 comprising the amino acid sequence of SEQ ID NO:39. For example, in an embodiment of the invention, the antibody or antigen-binding fragment comprises a heavy chain variable region comprising the amino acid sequence set forth in SEQ ID NO:8; and a light chain variable region comprising the amino acid sequence set forth in SEQ ID NO:9; or a heavy chain variable region comprising the amino acid sequence set forth in SEQ ID NO:16; and a light chain variable region comprising the amino acid sequence set forth in SEQ ID NO:17; or a heavy chain variable region comprising the amino acid sequence set forth in SEQ ID NO:24; and a light chain variable region comprising the amino acid sequence set forth in SEQ ID NO:25; or a heavy chain variable region comprising the amino acid sequence set forth in SEQ ID NO:32; and a light chain variable region comprising the amino acid sequence set forth in SEQ ID NO:33. For example, the present invention provides an antibody or antigen-binding fragment thereof that competes with DX435, DX439 and DX440 or with DX446 for binding to ILT3. The present invention further provides a multispecific (e.g., bispecific) antibody or antigen-binding fragment thereof that specifically binds to ILT3 and ILT3 ligand. Also provided is a composition comprising an antibody or antigen-binding fragment thereof that specifically binds to ILT3 and an antibody or antigen-binding fragment thereof that specifically binds to ILT3 ligand.

The present invention further provides a complex between ILT3 and ILT3 ligand (e.g., PI16), e.g., wherein the ILT3 or ILT3 ligand or both is on the surface of a cell (PI16 on a T-cell and/or ILT3 on a dendritic cell (DC), monocyte, macrophage, or vascular endothelial cell (EC)), detectably labeled (e.g., with a FRET acceptor or FRET donor), bound to a metal surface (e.g., gold or silver), bound to an antibody or antigen-binding fragment, or bound to an insoluble substrate.

The present invention also provides a method for forming a complex between ILT3 and ILT3 ligand (e.g., PI16) comprising contacting the ILT3 and ILT3 ligand under conditions favorable to complex formation; as well as the complex that is the product of this method.

In addition, the present invention provides a method for cross-linking two cells (e.g., a T-cell with a dendritic cell, monocyte, macrophage or vascular endothelial cell) comprising contacting one cell that expresses ILT3 on the cell surface and another cell that expresses ILT3 ligand (e.g., PI16) on the cell surface with a multispecific (e.g., bispecific) antibody or antigen-binding fragment thereof that specifically binds to said ILT3 and said ILT3 ligand.

A method for determining whether ILT3 and an ILT3 ligand (e.g., PI16) bind together is also part of the present invention. The method comprises contacting ILT3 ligand with ILT3 and determining whether the ILT3 ligand and the ILT3 form a complex; wherein, if a complex between the ILT3 ligand and the ILT3 is detected, then the ILT3 ligand and the ILT3 are determined to bind. In an embodiment of the invention, the ILT3 is detectably labeled and wherein the complex is detected by detecting the label bound to the ILT3 ligand; or wherein ILT3 ligand is detectably labeled and wherein the complex is detected by detecting the label bound to the ILT3. In an embodiment of the invention, the ILT3 is labeled with a FRET (fluorescence resonance energy transfer) acceptor and ILT3 ligand is labeled with a FRET donor; or ILT3 is labeled with a FRET donor and ILT3 ligand is labeled with a FRET acceptor; and wherein the complex is determined to form if FRET between the acceptor and donor is detected. In an embodiment of the invention, the ILT3, which is bound to a gold or silver metal surface which is on the surface of a glass slide, in contacted with ILT3 ligand and the metal is illuminated, through the glass, with polarized light wherein, if a change in the refractive index of medium in close vicinity to the metal surface illuminated with the light is detected, then the complex is determined to form; or ILT3 ligand, that is bound to a gold or silver metal surface which is on the surface of a glass slide, in contacted with ILT3 and the metal is illuminated, through the glass, with polarized light wherein, if a change in the refractive index of medium in close vicinity to the metal surface illuminated with the light is detected, then the complex is determined to form.

The present invention also provides a method for determining whether ILT3 and an ILT3 ligand (e.g., PI16) bind together comprising contacting ILT3 ligand that is expressed on the surface of a macrophage cell with ILT3 that is fused to a cytosolic domain of CD3 zeta and is expressed on the surface of a T-cell (e.g., Jurkat cell) that comprises an NFAT promoter operably linked to a reporter gene (e.g., luciferase) wherein binding is determined if reporter gene expression in the T-cell is detected.

The present invention further provides a method for determining whether a substance (e.g., an antibody) agonizes or antagonizes binding between ILT3 and ILT3 ligand (e.g., PI16) comprising contacting ILT3 ligand with ILT3 in the presence of the substance and determining whether the ILT3 ligand and the ILT3 form a complex; wherein the substance is determined to agonize said binding if more of the complex is determined in the presence of the substance than in the absence of the substance and wherein the substance is determined to antagonize said binding if less of the complex is determined in the presence of the substance than in the absence of the substance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1. Cell microarray technology was used to identify specific binding partners for ILT3Fc-fusion protein. 10 μg/ml of ILT3Fc was used for the binding screen against 3559 human plasma membrane proteins, each individually expressed in human HEK293 cells. The primary hit was re-expressed and re-tested with ILT3Fc and controls. The confirmation screen yielded six potential hits, including NIPA1 (non-imprinted in Prader-Willi/Angelman syndrome 1), PODXL2 (Podocalyxin-Like 2), MAG (Myelin Associated Glycoprotein), VSIG1 (V-set and immunoglobulin domain containing 1), PI16 (Peptidase inhibitor 16), and CLDN3 (Claudin3).

FIG. 2. The potential hits were validated by transient expression of cDNA vectors on 293T cells and co-culture with an ILT3 signaling reporter cell line. FcγR2B vector transfected cells served as a control. An ILT3 reporter cell line was constructed by fusing the extracellular domains of ILT3 with the intracellular signaling domain of CD3z chain. The reporter cells also contained an NFAT transcription factor-dependent luciferase gene. Upon ILT3-CD3z co-ligation, NFAT activation led to transcription and production of luciferase.

FIG. 3. cDNA vectors of the 6 potential hits were transiently expressed on HEK293T cells. Transfected cells (3e5: 2 fold titration) were co-cultured with ILT3-CD3z-luciferase reporter cells. PI16 expressed on the 293T cells activated ILT3 associated CD3z-NFAT-Luciferase activity (data shown; grey diamonds). None of the other expression vectors including FcγR2B control vector or vector-only control induced luciferase activity.

FIG. 4. Three isoforms of PI16 include a long form with CPI (glycophosphatidylinositol) C-terminal anchor sequence (pI16_Q6UXB8_1; SEQ ID NO:2), a short form, which is a splice variant with deletion of 232 to 424 amino acids but retaining the CPI C-terminal anchor sequence (PI16_Q6UXB8_2; SEQ ID NO:3), and finally, a nearly full length form of 408 amino acids and lacking the CPI C-terminal anchor sequence (PI16 Retrogenix; SEQ ID NO:4).

FIG. 5. A cartoon showing 3A9 cells that had been transfected with cDNA encoding PI16 expressing PI16 on the cell surface and ILT3Fc Immune Complex comprising ILT3Fc cross-linked to goat anti-human IgG Fc gamma specific antibody to form an ILT3Fc Immune Complex. The cells expressing PI16 are then reacted with the ILT3Fc Immune Complex and the bound ILT3Fc Immune Complex was detected with goat anti-mouse IgG, F(ab′)₂ PE conjugated antibody. Mouse VISTA-Fc was used as an irrelevant control.

FIG. 6. Top panel shows ILT3Fc (but not mouse VISTA-Fc) binds PI16 transfectin (8.3%). When ILT3Fc was cross-linked with mouse anti-human Fc mAb, the staining increased to 23%. The mouse anti-human Fc did not bind the PI16 expressing cells in the absence of ILT3Fc (0.17%). Lower panels show ILT3Fc titration from10 μg/mL to 0.16 μg/mL. PE-labelled Goat anti-human IgG Fc gamma-specific antibody was used as a second step stain. Mouse VISTA-Fc was an irrelevant control and the parental 3A9 cells transfected with control vector do not bind ILT3Fc.

FIG. 7. Major N-linked glycans produced in glycoengineered Pichia pastoris host cells and in Chinese hamster ovary cells (CHO).

FIG. 8. CD34 humanized mice (NSG mice, The Jackson Laboratory) were injected subcutaneously on the left flank with 1.5×10⁶ SKMEL5 tumor cells, a melanoma line obtained from ATCC. A phenotypic profile of human CD11b+ myeloid cells in spleen and tumor from SK-MEL-5 tumor bearing mice. Proportions of CD11b+ myeloid cells expressing ILT3 and ILT11 were determined. Result showed that ILT3 and ILT11 were expressed on a different subset of CD11b+ myeloid cells.

FIG. 9. Anti-ILT3 (DX446) treatment led to tumor growth inhibition. Tumor growth was measured in CD34 stem cell engrafted humanized mice transplanted with SKMEL5 and treated with either isotype (n=4, white circles), or DX446 (n=4, black circles) at 50 mpk. Two out of the 4 tumors in the DX446 treated groups regressed, while the other 2 tumors showed growth inhibition. Error bars represent SEM.

FIG. 10. Anti-ILT3 (DX446) treatment of SKMEL5 tumor bearing mice reduced the number of CD11b+, ILT3+, CD33+ myeloid cells. Splenocytes from either isotype or DX446 treated mice were isolated. Cells were stained with anti-ILT3, anti-ILT11 and anti-CD33 antibodies and analyzed by flow cytometry. Expression of ILT3, ILT11 and CD33 on myeloid cells, gated as CD11b+ cells is shown.

FIG. 11. Anti-PD1 activated T cells have enhanced PI16 expression. Humanized mice (CD34+ hematopoietic stem cells engrafted NSG mice) transplanted with PANC08 human pancreatic tumor cells were treated with isotype control antibody or anti-PD1 antibody, Pembrolizumab. Spleen cells were isolated, stained with CD3, CD4, CD8 and anti-PI16, and analyzed by flow cytometry. PI16+ CD3+ CD8+ cells have lower level of TIGIT (a T cell exhaustion marker) and higher level of Granzyme B (cytotoxic T cell marker) compared to PI16 negative cells.

FIG. 12. Identification of anti-PI16 antibodies that blocked ILT3Fc binding to a PI16 transfected cell line: nine antibodies were shown to bind CHO cells expressing cell surface recombinant PI16 (top panel). To identify antibodies that can block ILT3Fc binding to PI16, 3A9 cells were transfected with PI16 cDNA vector and then subjected to staining with ILT3Fc to bind PI16 expressed on the cell surface. Goat anti-human Fc antibody was used as a secondary staining antibody. Five of the anti-PI16 antibodies including clone 20B5, 44A5, 10E3, 49A7, and 20G8 blocked PI16+ cell binding to ILT3Fc. These antibody clones engage critical contact residues between PI16 and ILT3. Clones 34A1, 10H9, and 48A4 did not block PI16+ cell binding to ILT3Fc, indicating that 34A1, 10H9, and 48A4 engage PI16 epitope(s) not relevant for binding to ILT3.

FIG. 13. PI16-mediated suppression of ILT3+ dendritic cells is reversed by PI16 antagonist antibodies. Healthy human donor CD14+ monocytes were differentiated into dendritic cells by culturing in GMCSF and IL4 for 6 days and stimulated with IFNγ and LPS 24 hours prior to the assay. Recombinant PI16 bound to wells of a 96 well plates was incubated with control antibody or anti-PI16 antibodies for 30 minutes, washed, and activated dendritic cells were added. Following 72 hour stimulation, cells were analyzed for CD86 expression and TNF production. Anti-PI16 clones 49A7 and 10E3 (ILT3 blockers) “de-repressed” PI16 suppression of human dendritic cells by enhancing TNF and CD86 expression. Clone 34A1, which is a non-ILT3-blocker (See FIG. 12) did not enhance dendritic cells activation

=activated dendridic cells (DC); Δ=PI16;

=antibody.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides PI16, a heretofore an unknown ligand for ILT3. Knowledge of the identity of the ligand for ILT3 is useful as a means for identifying modulators of ILT3 and ILT3 ligand. Such modulators may be used, for example, for therapies for treating diseases such as cancer.

“Isolated” antibodies or antigen-binding fragments thereof, polypeptides, polynucleotides and vectors, are at least partially free of other biological molecules from the cells or cell culture from which they are produced. Such biological molecules include nucleic acids, proteins, lipids, carbohydrates, or other material such as cellular debris and growth medium. An isolated antibody or antigen-binding fragment may further be at least partially free of expression system components such as biological molecules from a host cell or of the growth medium thereof. Generally, the term “isolated” is not intended to refer to a complete absence of such biological molecules or to an absence of water, buffers, or salts or to components of a pharmaceutical formulation that includes the antibodies or fragments.

TABLE 1 Exemplary Conservative Amino Acid Substitutions Original residue Conservative substitution Ala (A) Gly; Ser Arg (R) Lys; His Asn (N) Gln; His Asp (D) Glu; Asn Cys (C) Ser; Ala Gln (Q) Asn Glu (E) Asp; Gln Gly (G) Ala His (H) Asn; Gln Ile (I) Leu; Val Leu (L) Ile; Val Lys (K) Arg; His Met (M) Leu; Ile; Tyr Phe (F) Tyr; Met; Leu Pro (P) Ala Ser (S) Thr Thr (T) Ser Trp (W) Tyr; Phe Tyr (Y) Trp; Phe Val (V) Ile; Leu

The following references relate to BLAST algorithms often used for sequence analysis: BLAST ALGORITHMS: Altschul et al. (2005) FEBS J. 272(20): 5101-5109; Altschul, S. F., et al., (1990) J. Mol. Biol. 215:403-410; Gish, W., et al., (1993) Nature Genet. 3:266-272; Madden, T. L., et al., (1996) Meth. Enzymol. 266:131-141; Altschul, S. F., et al., (1997) Nucleic Acids Res. 25:3389-3402; Zhang, J., et al., (1997) Genome Res. 7:649-656; Wootton, J. C., et al., (1993) Comput. Chem. 17:149-163; Hancock, J. M. et al., (1994) Comput. Appl. Biosci. 10:67-70; ALIGNMENT SCORING SYSTEMS: Dayhoff, M. O., et al., “A model of evolutionary change in proteins.” in Atlas of Protein Sequence and Structure, (1978) vol. 5, suppl. 3. M. O. Dayhoff (ed.), pp. 345-352, Natl. Biomed. Res. Found., Washington, D.C.; Schwartz, R. M., et al., “Matrices for detecting distant relationships.” in Atlas of Protein Sequence and Structure, (1978) vol. 5, suppl. 3.” M. O. Dayhoff (ed.), pp. 353-358, Natl. Biomed. Res. Found., Washington, D.C.; Altschul, S. F., (1991) J. Mol. Biol. 219:555-565; States, D. J., et al., (1991) Methods 3:66-70; Henikoff, S., et al., (1992) Proc. Natl. Acad. Sci. USA 89:10915-10919; Altschul, S. F., et al., (1993) J. Mol. Evol. 36:290-300; ALIGNMENT STATISTICS: Karlin, S., et al., (1990) Proc. Natl. Acad. Sci. USA 87:2264-2268; Karlin, S., et. al., (1993) Proc. Natl. Acad. Sci. USA 90:5873-5877; Dembo, A., et al., (1994) Ann. Prob. 22:2022-2039; and Altschul, S. F. “Evaluating the statistical significance of multiple distinct local alignments.” in Theoretical and Computational Methods in Genome Research (S. Suhai, ed.), (1997) pp. 1-14, Plenum, New York.

In an embodiment of the invention, the BLAST parameters used when determining the degree of similarity or identity between two sequences are: expect threshold: 10; word size: 3; max matches in a query range: 0; BLOSUM 62 matrix; gap costs: existence 11, extension 1; conditional compositional score matrix adjustment.

Sequence identity refers to the degree to which the amino acids of two polypeptides are the same at equivalent positions when the two sequences are optimally aligned. Sequence similarity includes identical residues and nonidentical, biochemically related amino acids. Biochemically related amino acids that share similar properties and may be interchangeable are discussed in Table 1.

As used herein “specifically binds” refers, with respect to an antigen or molecule such as human ILT3, to the preferential association of an antibody or other ligand, in whole or part, with human ILT3 and not to other molecules, particularly molecules found in human blood or serum. Antibodies typically bind specifically to their cognate antigen with high affinity, reflected by a dissociation constant (KD) of 10⁻⁷ to 10⁻¹¹ M or less. Any KD greater than about 10⁻⁶ M is generally considered to indicate nonspecific binding. As used herein, an antibody that “binds specifically” to an antigen refers to an antibody that binds to the antigen and substantially identical antigens with high affinity, which means having a KD of 10⁻⁷ M or less, in particular embodiments a KD of 10⁻⁸ M or less, or 5×10⁻⁹ M or less, or between 10⁻⁸ M and 10⁻¹¹ M or less, but does not bind with high affinity to unrelated antigens.

PI16 and ILTs

ILT3 (Immunoglobulin-like transcript 3) is also known by the names LILRB4, CD85K, LIR-5, and leukocyte immunoglobulin like receptor B4. Human ILT3 precursor protein comprises the amino acid sequence set forth in SEQ ID NO: 1. In the mature form of the human ILT3 molecule, the amino acid sequence lacks the 21 amino acid N-terminal signal (leader) sequence (SEQ ID NO:41). The extracellular domain of the human ILT3 comprises amino acids 22-238 of SEQ ID NO:1.

Human PI16 is also known as Peptidase inhibitor 16, CRISPS or PSPBP. In an embodiment of the invention, human PI16 exists in three isoforms: long (full length) isoform, short isoform, and a secreted isoform. The long isoform precursor amino acid sequence is shown in SEQ ID NO:2 and the amino acid sequence of the mature form lacking the 27 amino acid signal sequence is shown in SEQ ID NO:42. The short isoform precursor amino acid sequence is shown in SEQ ID NO:3 and the the amino acid sequence of the mature form lacking the 27 amino acid signal sequence is shown in SEQ ID NO:43. The short isoform lacks amino acids 232 through 424. The secreted isoform precursor amino acid sequence is shown in SEQ ID NO:4 and the amino acid sequence of the mature form lacking the 27 amino acid signal sequence is shown in SEQ ID NO:44. The secreted isoform lacks the C-terminal glycophosphatidylinositol (GPI) anchor sequence.

Human ILT11 (also known as LILRA5) precursor comprises the amino acid sequence shown in SEQ ID NO:6 and SEQ ID:45 shows the mature form lacking the 41 amino acid signal sequence.

Human ILT8 (also known as LILRA6) comprises the amino acid sequence shown in SEQ ID NO:7 and SEQ ID:46 shows the mature form lacking the 21 amino acid signal sequence.

The present invention includes a complex between ILT3 and ILT3 ligand (e.g., PI16), for example, in the presence of an antibody or antigen-binding fragment thereof that binds to the ILT3/PI16 complex, or ILT3 or PI16 or both. In an embodiment of the invention, an antibody or fragment binds the ILT3/ILT3 ligand complex but not to ILT3 or ILT3 ligand alone.

ILT3 or an ILT3 ligand includes variants as well as fragments (e.g., truncations) thereof which comprise sequence identity/similarity to ILT3 or ILT3 ligand and which are capable for forming a complex. A “variant” of a polypeptide (e.g., ILT3 or ILT3 ligand (e.g., PI16)) comprises an amino acid sequence that is at least about 70-99.9% (e.g., 70, 72, 74, 75, 76, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 99.5, 99.9%) identical or similar to a referenced amino acid sequence such as SEQ ID NO:1, 2, 3 or 4 that is set forth herein; when the comparison is performed by a BLAST algorithm wherein the parameters of the algorithm are selected to give the largest match between the respective sequences over the entire length of the respective reference sequences (e.g., expect threshold: 10; word size: 3; max matches in a query range: 0; BLOSUM 62 matrix; gap costs: existence 11, extension 1; conditional compositional score matrix adjustment). In an embodiment of the invention, the ILT3 or ILT3 ligand variant comprises 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 substitutions, e.g., conservative substitutions, for example, relative to that of SEQ ID NO:1, 2, 3 or 4. As used herein, the term ILT3 ligand excludes CD166.

Antibodies and Antigen-Binding Fragments Thereof

The present invention provides antibodies and antigen-binding fragments thereof that bind to ILT3 (e.g., human ILT3) or an ILT3 ligand (e.g., PI16 (e.g., human PI16)) or both or to a complex between ILT3 and ILT3 ligand (e.g., PI16). Such antibodies or fragments, in an embodiment of the invention, antagonize or agonize the binding between ILT3 and ILT3 ligand (e.g., PI16).

The present invention includes multispecific antibodies and antigen-binding fragments thereof that bind to both ILT3 and ILT3 ligand (e.g., PI16). Multispecific (e.g., bispecific) antibodies that bind to both ILT3 ligand (e.g., PI16) on a macrophage and ILT3 on a T-cell, and, for example, enhance the association between the macrophage and T-cell are also within the scope of the present invention, as is such a cell/ multispecific antibody complex.

In an embodiment of the invention, an antibody or antigen-binding fragment thereof of the present invention specifically binds to ILT3, but also binds to ILT3, ILT8 and/or ILT11 and/or, in an embodiment of the invention, does not bind specifically to ILT4. In an embodiment of the invention, such an antibody or antigen-binding fragment, which specifically binds to ILT3, ILT8 and/or ILT11, but not to ILT4 is DX446, DX435, DX439 or DX440. In an embodiment of the invention, the antibody is a variant of DX446, DX435, DX439 or DX440 having a heavy chain CDR1, CDR2 and/or CDR3 that comprises the amino acid sequence set forth in Table 2 or an amino acid having at least about 90% (e.g., 91, 92, 93, 94, 95, 096, 97, 98, 99%) amino acid sequence identity or similarity thereto or having 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 conservative amino acid substitutions relative to the corresponding amino acid sequence set forth in Table 2. In an embodiment of the invention, the antibody is a variant of DX446, DX435, DX439 or DX440 having a light chain CDR1, CDR2 and/or CDR3 that comprises the amino acid sequence set forth in Table 2 or an amino acid having at least about 90% (e.g., 91, 92, 93, 94, 95, 096, 97, 98, 99%) amino acid sequence identity or similarity thereto or having 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 conservative amino acid substitutions relative to the corresponding amino acid sequence set forth in Table 2. In an embodiment of the invention, the antibody is a variant of DX446, DX435, DX439 or DX440 having a light chain variable region that comprises the amino acid sequence set forth in Table 2 or an amino acid having at least about 90% (e.g., 91, 92, 93, 94, 95, 096, 97, 98, 99%) amino acid sequence identity or similarity thereto or having 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 conservative amino acid substitutions relative to the corresponding amino acid sequence set forth in Table 2. In an embodiment of the invention, the antibody is a variant of DX446, DX435, DX439 or DX440 having a heavy chain variable region that comprises the amino acid sequence set forth in Table 2 or an amino acid having at least about 90% (e.g., 91, 92, 93, 94, 95, 096, 97, 98, 99%) amino acid sequence identity or similarity thereto or having 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 conservative amino acid substitutions relative to the corresponding amino acid sequence set forth in Table 2.

An “anti-ILT3/ILT3 ligand” (e.g., “anti-ILT3/PI16”) antibody or antigen-binding fragment binds to both ILT3 and ILT3 ligand and, optionally, to another epitope. The term includes multispecific (e.g., bispecific) antibodies and antigen-binding fragments.

Antagonism of binding between ILT3 ligand (e.g., PI16) and ILT3 refers to reduction of such binding, e.g., as measured by any assay such as an in vitro cell binding assay between two cells expressing ILT3 and ILT3 ligand (e.g., PI16). Also, agonism of binding between ILT3 ligand (e.g., PI16) and ILT3 refers to the increase of such binding, e.g., as measured by any assay such as an in vitro cell binding assay between two cells expressing ILT3 and ILT3 ligand (e.g., PI16). Antagonism or agonism of binding can be determined using any of the methods for determining such binding that are discussed herein.

A multivalent antibody or antigen-binding fragment is an antibody or fragment comprising two or more antigen binding sites. A bivalent antibody or antigen-binding fragment includes, for example, a full antibody which has two antigen-binding arms. The present invention includes multivalent, e.g., bivalent antibodies and antigen-binding fragments thereof.

A multispecific antibody or antigen-binding fragment thereof binds to more than one epitope, e.g., 2, 3 or 4. For example, a bispecific antibody is an example of a multispecific antibody. The present invention includes such multispecific antibodies and fragments that bind to ILT3 and ILT3 ligand (e.g., PI16) and, optionally, to another epitope.

In general, the basic antibody structural unit comprises a tetramer. Each tetramer includes two identical pairs of polypeptide chains, each pair having one “light” (about 25 kDa) and one “heavy” chain (about 50-70 kDa). The amino-terminal portion of each chain includes a variable region of about 100 to 110 or more amino acids primarily responsible for antigen recognition. The carboxy-terminal portion of the heavy chain may define a constant region primarily responsible for effector function. Typically, human light chains are classified as kappa and lambda light chains. Furthermore, human heavy chains are typically classified as mu, delta, gamma, alpha, or epsilon, and define the antibody's isotype as IgM, IgD, IgG, IgA, and IgE, respectively. Within light and heavy chains, the variable and constant regions are joined by a “J” region of about 12 or more amino acids, with the heavy chain also including a “D” region of about 10 more amino acids. See generally, Fundamental Immunology Ch. 7 (Paul, W., ed., 2nd ed. Raven Press, N.Y. (1989).

The present invention includes monoclonal anti-ILT3, anti-ILT3 ligand (e.g., anti-PI16) and anti-ILT3/ILT3 ligand (e.g., anti-ILT3/PI16) antibodies and antigen-binding fragments thereof including multispecific antibodies and fragments as well as monoclonal compositions comprising a plurality of isolated monoclonal antibodies and antigen-binding fragments thereof. The term “monoclonal antibody”, as used herein, refers to a population of substantially homogeneous antibodies, i.e., the antibody molecules comprising the population are identical in amino acid sequence except for possible naturally occurring mutations that may be present in minor amounts. A “plurality” of such monoclonal antibodies and fragments in a composition refers to a concentration of identical (i.e., as discussed above, in amino acid sequence except for possible naturally occurring mutations that may be present in minor amounts) antibodies and fragments which is above that which would normally occur in nature, e.g., in the blood of a host organism such as a mouse or a human. In contrast, conventional (polyclonal) antibody preparations typically include a multitude of different antibodies having different amino acid sequences in their variable domains, particularly their CDRs, that are often specific for different epitopes. The modifier “monoclonal” indicates the character of the antibody as being obtained from a substantially homogeneous population of antibodies, and is not to be construed as requiring production of the antibody by any particular method. For example, the monoclonal antibodies to be used in accordance with the present invention may be made by the hybridoma method first described by Kohler et al., Nature 256: 495 (1975), or may be made by recombinant DNA methods (see, e.g., U.S. Pat. No. 4,816,567). The “monoclonal antibodies” may also be isolated from phage antibody libraries using the techniques described in Clackson et al., Nature 352: 624-628 (1991) and Marks et al., J. Mol. Biol. 222: 581-597 (1991), for example. See also Presta, J. Allergy Clin. Immunol., 116:731 (2005).

The present invention includes anti-ILT3, anti-ILT3 ligand (e.g., anti-PI16) and anti-ILT3/ILT3 ligand (e.g., anti-ILT3/PI16) chimeric antibodies (e.g., human constant domain/mouse variable domain) and methods of use thereof. As used herein, a “chimeric antibody” is an antibody having the variable domain from a first antibody and the constant domain from a second antibody, where the first and second antibodies are from different species. (U.S. Pat. No. 4,816,567; and Morrison et al., Proc. Natl. Acad. Sci. USA 81: 6851-6855 (1984)). Typically, the variable domains are obtained from an antibody from an experimental animal (the “parental antibody”), such as a rodent, and the constant domain sequences are obtained from human antibodies, so that the resulting chimeric antibody will be less likely to elicit an adverse immune response in a human subject than the parental (e.g., mouse) antibody.

The present invention includes anti-ILT3, anti-ILT3 ligand (e.g., anti-PI16) and anti-ILT3/ILT3 ligand (e.g., anti-ILT3/PI16) humanized antibodies and antigen-binding fragments thereof (e.g., mouse antibodies that have been humanized) and methods of use thereof. As used herein, the term “humanized antibody” refers to forms of antibodies that contain sequences from both human and non-human (e.g., mouse or rat) antibodies. In general, the humanized antibody will comprise substantially all of at least one, and typically two, variable domains, in which all or substantially all of the hypervariable loops correspond to those of a non-human immunoglobulin, and all or substantially all of the framework (FR) regions are those of a human immunoglobulin sequence. The humanized antibody may optionally comprise at least a portion of a human immunoglobulin constant region (Fc).

The present invention includes anti-ILT3, anti-ILT3 ligand (e.g., anti-PI16) and anti-ILT3/ILT3 ligand (e.g., anti-ILT3/PI16) recombinant antibodies and antigen-binding fragments thereof and methods of use thereof. There are several methods by which to produce recombinant antibodies which are known in the art. One example of a method for recombinant production of antibodies is disclosed in U.S. Pat. No. 4,816,567.

The present invention includes anti-ILT3, anti-ILT3 ligand (e.g., anti-PI16) and anti-ILT3/ILT3 ligand (e.g., anti-ILT3/PI16) fully human antibodies and antigen-binding fragments thereof and methods of use thereof. The term “fully human antibody” refers to an antibody that comprises human immunoglobulin protein sequences only. A fully human antibody may contain murine carbohydrate chains if produced in a mouse, in a mouse cell, or in a hybridoma derived from a mouse cell. Similarly, “mouse antibody” refers to an antibody that comprises mouse immunoglobulin sequences only. Alternatively, a fully human antibody may contain rat carbohydrate chains if produced in a rat, in a rat cell, or in a hybridoma derived from a rat cell. Similarly, “rat antibody” refers to an antibody that comprises rat immunoglobulin sequences only. In an embodiment of the invention, an fully human anti-ILT3, anti-PI16 and anti-ILT3/PI16 antibody or antigen-binding fragment thereof is the product of isolation from a transgenic animal, e.g., a mouse (e.g., a HUMAB mouse, see e.g., U.S. Pat. Nos. 5,545,806; 5,569,825; 5,625,126; 5,633,425; 5,661,016; 5,770,429; 5,789,650; 5,814,318; 5,874,299 and 5,877,397; and Harding, et al., (1995) Ann. NY Acad. Sci. 764:536 546; or a XENOMOUSE, see e.g., Green et al., 1999, J. Immunol. Methods 231:11-23), which has been genetically modified to have fully human immunoglobulin genes; or the product of isolation from a phage or virus which expresses the immunoglobulin chains.

The present invention includes anti-ILT3, anti-ILT3 ligand (e.g., anti-PI16) and anti-ILT3/ILT3 ligand (e.g., anti-ILT3/PI16) antigen-binding fragments and methods of use thereof. As used herein, unless otherwise indicated, “antibody fragment” or “antigen-binding fragment” refers to antigen-binding fragments of antibodies, i.e. antibody fragments that retain the ability to bind specifically to the antigen bound by the full-length antibody, e.g. fragments that retain one or more CDR regions. Examples of antigen-binding fragments include, but are not limited to, Fab, Fab′, F(ab′)₂, and Fv fragments; diabodies; single-chain antibody molecules, e.g., sc-Fv and multispecific antibodies formed from antibody fragments.

The present invention includes anti-ILT3, anti-ILT3 ligand (e.g., anti-PI16) and anti-ILT3/ILT3 ligand (e.g., anti-ILT3/PI16) Fab fragments and methods of use thereof. A “Fab ragment” is comprised of one light chain and the C_(H)1 and variable regions of one heavy chain. The heavy chain of a Fab molecule cannot form a disulfide bond with another heavy chain molecule. An “Fab fragment” can be the product of papain cleavage of an antibody.

The present invention includes anti-ILT3, anti-PI16 and multispecific anti-ILT3/PI16 antibodies and antigen-binding fragments thereof which comprise an Fc region and methods of use thereof. An “Fc” region contains two heavy chain fragments comprising the C_(H)1 and C_(H)2 domains of an antibody. The two heavy chain fragments are held together by two or more disulfide bonds and by hydrophobic interactions of the C_(H)3 domains.

The present invention includes anti-ILT3, anti-ILT3 ligand (e.g., anti-PI16) and anti-ILT3/ILT3 ligand (e.g., anti-ILT3/PI16) Fab′ fragments and methods of use thereof. A “Fab′ fragment” contains one light chain and a portion or fragment of one heavy chain that contains the V_(H) domain and the C_(H)1 domain and also the region between the C_(H)1 and C_(H)2 domains, such that an interchain disulfide bond can be formed between the two heavy chains of two Fab′ fragments to form a F(ab′)₂ molecule.

The present invention includes anti-ILT3, anti-ILT3 ligand (e.g., anti-PI16) and anti-ILT3/ILT3 ligand (e.g., anti-ILT3/PI16) F(ab′)₂ fragments and methods of use thereof. A “F(ab′)₂ fragment” contains two light chains and two heavy chains containing a portion of the constant region between the C_(H1) and C_(H2) domains, such that an interchain disulfide bond is formed between the two heavy chains. A F(ab′)₂ fragment thus is composed of two Fab′ fragments that are held together by a disulfide bond between the two heavy chains. An “F(ab′)₂ fragment” can be the product of pepsin cleavage of an antibody.

The present invention includes anti-ILT3, anti-ILT3 ligand (e.g., anti-PI16) and anti-ILT3/ILT3 ligand (e.g., anti-ILT3/PI16) Fv fragments and methods of use thereof. The “Fv region” comprises the variable regions from both the heavy and light chains, but lacks the constant regions.

The present invention includes anti-ILT3, anti-ILT3 ligand (e.g., anti-PI16) and anti-ILT3/ILT3 ligand (e.g., anti-ILT3/PI16) scFv fragments and methods of use thereof. The term “single-chain Fv” or “scFv” antibody refers to antibody fragments comprising the V_(H) and V_(L) domains of an antibody, wherein these domains are present in a single polypeptide chain. Generally, the Fv polypeptide further comprises a polypeptide linker between the V_(H) and V_(L) domains which enables the scFv to form the desired structure for antigen-binding. For a review of scFv, see Pluckthun (1994) THE PHARMACOLOGY OF MONOCLONAL ANTIBODIES, vol. 113, Rosenburg and Moore eds. Springer-Verlag, New York, pp. 269-315. See also, International Patent Application Publication No. WO88/01649 and U.S. Pat. Nos. 4,946, 778 and 5,260,203.

Eukaryotic and prokaryotic host cells, including mammalian cells as hosts for expression of the anti-ILT3, anti-ILT3 ligand (e.g., anti-PI16) and anti-ILT3/ILT3 ligand (e.g., anti-ILT3/PI16) antibodies and antigen-binding fragments thereof and immunoglobulin chains thereof (e.g., heavy chain and/or light chain) disclosed herein are well known in the art and include many immortalized cell lines available from the American Type Culture Collection (ATCC). These include, inter alia, Chinese hamster ovary (CHO) cells, NSO, SP2 cells, HeLa cells, baby hamster kidney (BHK) cells, monkey kidney cells (COS), human hepatocellular carcinoma cells (e.g., Hep G2), A549 cells, 3T3 cells, HEK-293 cells and a number of other cell lines. Mammalian host cells include human, mouse, rat, dog, monkey, pig, goat, bovine, horse and hamster cells. Cell lines of particular preference are selected through determining which cell lines have high expression levels. Other cell lines that may be used are insect cell lines (e.g., Spodoptera frugiperda or Trichoplusia ni), amphibian cells, bacterial cells, plant cells and fungal cells. Fungal cells include yeast and filamentous fungus cells including, for example, Pichia pastoris, Pichia finlandica, Pichia trehalophila, Pichia koclamae, Pichia membranaefaciens, Pichia minuta (Ogataea minuta, Pichia lindneri), Pichia opuntiae, Pichia thermotolerans, Pichia salictaria, Pichia guercuum, Pichia pijeri, Pichia stiptis, Pichia methanolica, Pichia sp., Saccharomyces cerevisiae, Saccharomyces sp., Hansenula polymorpha, Kluyveromyces sp., Kluyveromyces lactis, Candida albicans, Aspergillus nidulans, Aspergillus niger, Aspergillus oryzae, Trichoderma reesei, Chrysosporium lucknowense, Fusarium sp., Fusarium gramineum, Fusarium venenatum, Physcomitrella patens and Neurospora crassa. Pichia sp., any Saccharomyces sp., Hansenula polymorpha, any Kluyveromyces sp., Candida albicans, any Aspergillus sp., Trichoderma reesei, Chrysosporium lucknowense, any Fusarium sp., Yarrowia lipolytica, and Neurospora crassa. Host cells including anti-ILT3, anti-ILT3 ligand and anti-ILT3/ILT3 ligand antibodies and antigen-binding fragments are part of the present invention.

Further, expression of antibodies and antigen-binding fragments thereof and immunoglobulin chains of the invention (or other moieties therefrom) from production cell lines can be enhanced using a number of known techniques. For example, the glutamine synthetase gene expression system (the GS system) is a common approach for enhancing expression under certain conditions. The GS system is discussed in whole or part in connection with European Patent Nos. 0 216 846, 0 256 055, and 0 323 997 and European Patent Application No. 89303964.4. Thus, in an embodiment of the invention, the mammalian host cells (e.g., CHO) lack a glutamine synthetase gene and are grown in the absence of glutamine in the medium wherein, however, the polynucleotide encoding the immunoglobulin chain comprises a glutamine synthetase gene which complements the lack of the gene in the host cell.

The present invention includes methods for purifying an anti-ILT3, anti-ILT3 ligand (e.g., anti-PI16) and anti-ILT3/ILT3 ligand (e.g., anti-ILT3/PI16) antibody or antigen-binding fragment thereof of the present invention comprising introducing a sample (e.g., culture medium, cell lysate or cell lysate fraction, e.g., a soluble fraction of the lysate) comprising the antibody or fragment to a purification medium (e.g., cation-exchange medium, anion-exchange medium, hydrophobic exchange medium, affinity purification medium (e.g., protein-A). In an embodiment of the invention, the medium is in a column to which the sample is applied. In an embodiment of the invention, the purification method is conducted following recombinant expression of the antibody or fragment in a host cell, e.g., wherein the host cell is first lysed and, optionally, the lysate is purified of insoluble materials prior to purification on a medium; or wherein the antibody or fragment is secreted into the culture medium by the host cell and the medium or a fraction thereof is applied to the purification medium.

The present invention includes anti-ILT3, anti-ILT3 ligand (e.g., anti-PI16) and anti-ILT3/ILT3 ligand (e.g., anti-ILT3/PI16) antibodies or antigen-binding fragments comprising N-linked glycans that are typically added to immunoglobulins produced in Chinese hamster ovary cells (CHO N-linked glycans) or to engineered yeast cells (engineered yeast N-linked glycans), such as, for example, Pichia pastoris. See FIG. 7. For example, in an embodiment of the invention, the antibody or antigen-binding fragment comprises one or more of the “engineered yeast N-linked glycans” or “CHO N-linked glycans” that are set forth in FIG. 8 (e.g., G0 and/or G0-F and/or G1 and/or G1-F and/or and/or G2-F and/or Man5). In an embodiment of the invention, the antibody or antigen-binding fragment comprises the engineered yeast N-linked glycans, i.e., G0 and/or G1 and/or G2, optionally, further including Man5. In an embodiment of the invention, the antibody or antigen-binding fragment comprise the CHO N-linked glycans, i.e., G0-F, G1-F and G2-F, optionally, further including G0 and/or G1 and/or G2 and/or Man5. In an embodiment of the invention, about 80% to about 95% (e.g., about 80-90%, about 85%, about 90% or about 95%) of all N-linked glycans on the antibody or antigen-binding fragment immunoglobulin chains are engineered yeast N-linked glycans or CHO N-linked glycans. See Nett et al. Yeast. 28(3): 237-252 (2011); Hamilton et al. Science. 313(5792): 1441-1443 (2006); Hamilton et al. Curr Opin Biotechnol. 18(5): 387-392 (2007). For example, in an embodiment of the invention, an engineered yeast cell is GFI5.0 or YGLY8316 or strains set forth in U.S. Pat. No. 7,795,002 or Zha et al. Methods Mol Biol. 988:31-43 (2013). See also international patent application publication no. WO2013/066765.

In one embodiment, the anti-ILT3, anti-ILT3 ligand (e.g., anti-PI16) and anti-ILT3/ILT3 ligand (e.g., anti-ILT3/PI16) antibodies or antigen-binding fragments comprises a heavy chain constant region, e.g. a human constant region, such as γ1, γ2, γ3, or γ4 human heavy chain constant region or a variant thereof. In another embodiment, the anti-ILT3, anti-PI16 or multispecific anti-ILT3/PI16 antibodies or antigen-binding fragments comprises a light chain constant region, e.g. a human light chain constant region, such as lambda or kappa human light chain region or variant thereof. In an embodiment of the invention, the Fc region of the antibody is γ4 with a Ser228Pro mutation (Schuurman, J et. al., Mol. Immunol. 38: 1-8, 2001).

In particular embodiments, the present invention provides the above antibody or antigen binding fragment wherein the antibody comprises a human IgG1, IgG2, IgG3, or IgG4 heavy chain (HC) constant domain or variant thereof comprising 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acid substitutions, additions, deletions, or combinations thereof compared to the amino acid sequence of the native IgG1, IgG2, IgG3, or IgG4 isotype.

In some embodiments, different constant domains may be fused to a V_(L) and V_(H) regions comprising the CDRs provided herein. In particular embodiments, the V_(L) and V_(H) regions comprising the CDRs provided herein may be fused to a human IgG1, IgG2, IgG3, or IgG4 heavy chain (HC) constant domain or variant thereof comprising 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acid substitutions, additions, deletions, or combinations thereof compared to the amino acid sequence of the native or wild-type IgG1, IgG2, IgG3, or IgG4 isotype.

In particular embodiments the anti-ILT3 antibody (or antigen binding fragment) has an altered effector function and may comprise a heavy chain constant domain other than native (wild-type) human IgG1, for example a human IgG1 that has mutations that abrogate or minimize one or more effector functions, including ability to bind complement, human IgG4, or a hybrid human IgG1/human IgG4.

Although native human IgG1 antibodies provide for long half-life and for effector functions, such as complement activation and antibody-dependent cellular cytotoxicity, such activities may not be desirable for all uses of an antibody. Thus, in particular embodiments, it is desirable that the heavy chain constant domain or Fc have minimal or reduced effector function (“effector-less”). In those instances, the anti-ILT3 HC variable domain may be fused to a human IgG4 constant domain, which is generally known to be effector-less, or an IgG1 constant domain that has been mutated to be rendered effecter-less. These effector-less molecules have minimal or reduced binding to human FcγRIIIA, and FcγRIIA, and Fcγ.RI compared to the polypeptide comprising the wildtype IgG Fc region, wherein the affinity to each of human FcγRIIIA, and FcγRIIA, and FcγRI is reduced by 1.15-fold to 100-fold compared to the polypeptide comprising the wildtype IgG constant domain, and wherein the antibody-dependent cell-mediated cytotoxicity (ADCC) induced by said molecule is 0-20% of the ADCC induced by the polypeptide comprising the wild-type human IgG1 constant domain.

Therefore in particular embodiments, the present invention includes chimeric or humanized anti-ILT3 antibodies and antigen-binding fragments thereof that comprise a human IgG4 constant domain. In a further embodiment, the human IgG4 constant domain may be modified to differ from the native (wild-type) human IgG4 constant domain (Swiss-Prot Accession No. P01861.1) at a position corresponding to position 228 in the EU system and position 241 in the KABAT system in which the native serine at position 108 (Ser108) of the HC constant domain is replaced with proline (Pro), see for example SEQ ID NO:56. This modification prevents formation of a potential inter-chain disulfide bond between the cysteine at position 106 (Cys106) and the cysteine at position 109 (Cys109), which correspond to positions Cys226 and Cys229 in the EU system and positions Cys239 and Cys242 in the KABAT system, which may interfere with proper intra-chain disulfide bond formation. See Angal et al. Mol. Imunol. 30:105 (1993); see also (Schuurman et. al., Mol. Immunol. 38: 1-8, (2001); SEQ ID NOs:14 and 41). In particular embodiments, the human IgG4 constant domain may further include in addition to the S228P substitution an L235E substitution.

In another embodiment, the chimeric or humanized anti-ILT3 antibody may be fused to a modified human IgG1 constant domain, which has been modified to be effector-less. In one embodiment, the human IgG1 HC may include substitutions of human IgG2 HC residues at positions 233-236 and IgG4 HC residues at positions 327, 330, and 331 to greatly reduce ADCC and CDC (Armour et al., Eur J Immunol. 29(8):2613-24 (1999); Shields et al., J Biol Chem. 276(9):6591-604(2001)). In particular embodiments, the antibody comprises a human IgG1 heavy chain (HC) constant domain or variant thereof comprising 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acid substitutions, additions, deletions, or combinations thereof compared to the amino acid sequence of the native IgG, which provides an antibody having reduced or minimal effector function. In particular aspects, the IgG1 has been modified to comprise or consist of an L234A, an L235A, and a D265S mutation to render the Fc effector-less (SEQ ID NO:57). Other mutations that may be used to render an IgG1 Fc effector-less may be found in U.S. Pat. No. 8,969,526.

In another embodiment, the human IgG1 HC is modified to lack N-glycosylation of the asparagine (Asn) residue at around position 297 of the HC. The consensus sequence for N-glycosylation is Asn-Xaa-Ser/Thr (wherein Xaa is any amino acid except Pro); in IgG1 the N-glycosylation consensus sequence is Asn-Ser-Thr. The modification may be achieved by replacing the codon for the Asn at position 297 in the nucleic acid molecule encoding the HC with a codon for another amino acid, for example Gln. Alternatively, the codon for Ser may be replaced with the codon for Pro or the codon for Thr may be replaced with any codon except the codon for Ser, e.g. N297A or N297D . Such modified IgG1 molecules have little or no detectable effector function. Alternatively, all three codons are modified.

In another embodiment, the human IgG1 constant domain is modified to include one or more amino acid substitutions selected from E233P, L234A, L235A, L235E, N297A, N297D, D265S, and P331S, wherein the residues are numbered according to the EU index of Kabat, and wherein said polypeptide exhibits a reduced affinity to the human FcγRIIIA and/or FcγRIIA and/or FcγRI compared to a polypeptide comprising the wildtype IgG constant domain region. In particular embodiments, the human IgG constant domain comprises substitutions of L234A, L235A, and D265S as illustrated by SEQ ID NO:57, for example. In particular embodiments, the human IgG1 constant domain comprises an amino acid substitution at position Pro329 and at least one further amino acid substitution E233P, L234A, L235A, L235E, N297A, N297D, D265S, and P331S. These and other substitutions are disclosed in WO9428027; WO2004099249; WO20121300831, U.S. Pat. Nos. 9,708,406; 8,969,526; 9,296,815; Sondermann et al. Nature 406, 267-273 (20 Jul. 2000)).

The present invention further provides a composition comprising any one of the aforementioned antibodies and a pharmaceutically acceptable carrier. In particular embodiments, the composition comprises a mixture of antibodies comprising a heavy chain having a C-terminal lysine and antibodies comprising a heavy chain lacking a C-terminal lysine. In particular embodiments, the composition comprises an antibody disclosed herein wherein the predominant antibody form comprises a heavy chain having a C-terminal lysine. In particular embodiments, the composition comprises an antibody disclosed herein wherein the predominant antibody form comprises a heavy chain lacking a C-terminal lysine. In particular embodiments, the composition comprises an antibody disclosed herein wherein about 100% of the antibodies in the composition comprise a heavy chain lacking a C-terminal lysine.

Assays

The present invention includes a method for forming a complex between ILT3 ligand (e.g., PI16) and ILT3 comprising contacting the ILT3 and ILT3 ligand (e.g., PI16) under conditions favorable to binding and complex formation. In an embodiment of the invention, the ILT3 is on the surface of a cell such as a macrophage. In an embodiment of the invention, the ILT3 ligand (e.g., PI16) is on the surface of a cell such as a T-cell. In an embodiment of the invention, the ILT3 and/or ILT3 ligand (e.g., PI16) is not on the surface of a cell, e.g., is soluble or tethered to an insoluble support (e.g., polycarbonate, polystyrene, polypropylene, polyethlene, glass, nitrocellulose, dextran, nylon, polyacrylamide or agarose). In an embodiment of the invention, the ILT3 is labeled with a FRET donor and the ILT3 ligand is labeled with FRET acceptor; or the ILT3 ligand is labeled with a FRET donor and the ILT3 is labeled with FRET acceptor. In an embodiment of the invention, the ILT3 or ILT3 ligand is bound to a metal surface (e.g., gold or silver metal) on an transparent surface (e.g., glass slide). In an embodiment of the invention, the ILT3 and/or ILT3 ligand in the complex is bound to one or more antibodies or antigen-binding fragments thereof (e.g., anti-ILT3, anti-ILT3 ligand or bispecific anti-LT3/ILT3 ligand). Complexes comprising such ILT3 and ILT3 ligand are part of the present invention. In an embodiment of the invention, the complex is the product of a process of forming the complex as described herein.

The present invention also provides a method for determining whether ILT3 and ILT3 ligand (e.g., PI16) bind together, for example, under a given set of test conditions, e.g., in the presence of a test substance or at a given pH, salt concentration, temperature or buffer concentration. In an embodiment of the invention, the method comprises contacting said ILT3 ligand (e.g., PI16) with said ILT3 under the conditions to be tested and determining binding between the ILT3 ligand (e.g., PI16) and ILT3. If a complex between ILT3 ligand (e.g., PI16) and ILT3 is present, then the ILT3 ligand (e.g., PI16) and ILT3 are determined to bind under those conditions (e.g., in the presence of the test substance). In an embodiment of the invention, the ILT3 or ILT3 ligand (e.g., PI16) or both are on a cell surface, e.g., wherein ILT3 ligand (e.g., PI16) is on a T-cell surface and/or wherein ILT3 is on the macrophage cell surface. In an embodiment of the invention, the ILT3 or ILT3 ligand (e.g., PI16) or both are not on a cell surface, e.g., are soluble or are bound to a solid, insoluble substrate (e.g., polycarbonate, polystyrene, polypropylene, polyethlene, glass, nitrocellulose, dextran, nylon, polyacrylamide or agarose).

Methods for determining whether a substance agonizes or antagonizes such binding can also be performed by determining such binding in the presence of the substance; wherein the substance antagonizes the binding if less binding is observed in the presence of the substance than in the absence of the substance; and the substance agonizes the binding if more binding is observed in the presence of the substance than in the absence of the substance. Such substances can be tested for agonism or antagonism using any of the binding assay methods set forth herein.

The present invention can also be used to identify substances that reduce immune tolerance, reduce Ts (T suppressor cell) differentiation, reduce inhibition of CD4+ Th activation, reduce inhibition of CD8+ cytotoxic T lymphocyte (CTL) activation. Substances that antagonize ILT3/ILT3 ligand complex formation may be determined to have one or more of these characteristics.

A “substance” to be tested in an assay set forth herein can be a small organic molecule, an antibody or an antigen-binding fragment of an antibody.

The present invention provides a method for determining whether ILT3 binds with ILT3 ligand (e.g., PI16) comprising contacting a cell, e.g., a HEK293 cell or a 3A9 cell, that expresses PI16 on the cell surface, with ILT3 fused to an Fc that is bound by an anti-Fc antibody (e.g., anti-human IgG Fcγ-specific antibody) which is detectably labeled, e.g., with phycoerythrin, and determining whether the cell is labeled with the detectable label. If the cell is determined to be labeled with the detectable label, then the ILT3 and ILT3 ligand (e.g., PI16) are determined to bind.

A detectable label can be any label whose presence in a composition can be determined. For example, a detectable label can be a polypeptide to which, for example, ILT3 or ILT3 ligand (e.g., PI16) is fused, e.g., a radiolabel (e.g., ³H, ³⁵S, ³²P, ¹⁴C, or ¹³¹I), epitope tag (e.g., a FLAG tag such as DYKDDDDK (SEQ ID NO:5)), Fc, glutathione-S-transferase (GST).

The present invention provides a method for determining whether ILT3 binds with ILT3 ligand (e.g., PI16) comprising contacting a cell that expresses ILT3 ligand (e.g., PI16) on the cell surface, e.g., a human embryonic kidney cell (HEK293T) cell, with a cell that expresses ILT3 on the cell surface, e.g., a T-cell such as a Jurkat cell, wherein the ILT3 on the cell surface is fused to a cytosolic CD3z (CD3zeta) domain and wherein that cell includes a reporter gene, e.g., luciferase or green fluorescent protein (GFP), linked to a CD3z-responsive promoter (such as an NFAT (nuclear factor of activated T-cells) promoter). Cross-linking to CD3z induces NFAT promoter expression and, in turn, reporter expression. If expression of the reporter gene is detected, then the ILT3 and ILT3 ligand (e.g., PI16) are determined to bind.

The present invention provides a method for determining whether ILT3 binds with ILT3 ligand (e.g., PI16) by use of fluorescence resonance energy transfer (FRET). FRET utilizes energy transferred between donor and acceptor molecules that are in close proximity. If a ligand labeled with a FRET acceptor is bound to a receptor labeled with a FRET donor, then the acceptor will fluoresce when excited. In general, when using FRET, there should be a distance smaller than 10 nm between the acceptor and donor, in addition to an overlapping absorption spectrum between acceptor and donor. The method comprises labeling ILT3 with the acceptor and ILT3 ligand (e.g., PI16) with the donor (or vice versa), incubating the labeled ILT3 and labeled ILT3 ligand (e.g., PI16) and determining if there is light emitted as a result of fluorescence resonance energy transfer between the acceptor and donor. In an embodiment of the invention the donor/acceptor pair used in the method is as follows: fluorescein/tetramethylrhodamine; IAEDANS/fluorescein; EDANS/Dabcyl; fluorescein/fluorescein; BODIPY FL/BODIPY FL; fluorescein/QSY 7; or fluorescein/QSY 9 dyes.

The present invention provides a method for determining whether ILT3 binds with ILT3 ligand (e.g., PI16) by use of surface plasmon resonance (SPR). SPR does not require labeling of the ILT3 or ILT3 ligand. The surface plasmon resonance device is an optical biosensor that measures binding events of biomolecules (e.g., ILT3 and PI16) at a metal surface by detecting changes in the local refractive index. SPR technology exploits surface plasmons (electromagnetic waves) that can be excited at certain metal interfaces, e.g., silver and gold. When incident light is coupled with the metal interface at angles greater than the critical angle, the reflected light exhibits a sharp attenuation (SPR minimum) in reflectivity owing to the resonant transfer of energy from the incident light to a surface plasmon. Binding of the biomolecules at the surface changes the local refractive index and results in a shift of the SPR minimum. By monitoring changes in the SPR signal, it is possible to measure binding activities at the surface in real time. For example, binding of ILT3 on the surface by ILT3 ligand (or vice versa) will create an SPR signal. For example, ILT3, that is bound to a gold or silver metal surface which is on the surface of a glass slide, is contacted with ILT3 ligand (e.g., PI16) and the metal is illuminated, through the glass, with polarized light wherein, and, if a change in the refractive index of medium in close vicinity to the metal surface illuminated with the light is detected, then the complex is determined to form; or ILT3 ligand, that is bound to a gold or silver metal surface which is on the surface of a glass slide, is contacted with ILT3 and the metal is illuminated, through the glass, with polarized light wherein, if a change in the refractive index of medium in close vicinity to the metal surface illuminated with the light is detected, then the complex is determined to form.

The present invention provides a method for determining whether ILT3 binds with ILT3 ligand (e.g., PI16) by use of immunoprecipitation (IP). The method comprises contacting ILT3 and ILT3 ligand (e.g., PI16), binding the ILT3 with an antibody or antigen-binding fragment thereof which is immobilized to a solid phase (e.g., an insoluble bead or matrix such as agarose or glass); removing the bound ILT3 from the solid phase and determining the presence of ILT3 ligand (e.g., PI16) wherein the ILT3 and ILT3 ligand (e.g., PI16) are determined to bind if the ILT3 ligand (e.g., PI16) is detected in the presence of the ILT3. In an embodiment of the invention, the method comprises contacting ILT3 and ILT3 ligand (e.g., PI16), binding the ILT3 ligand (e.g., PI16) with an antibody or antigen-binding fragment thereof which is immobilized to a solid phase (e.g., an insoluble bead or matrix such as agarose or glass); removing the bound ILT3 ligand (e.g., PI16) from the solid phase and determining the presence of ILT3 wherein the ILT3 and ILT3 ligand (e.g., PI16) are determined to bind if the ILT3 is detected in the presence of the ILT3 ligand (e.g., PI16).

Pharmaceutical Compositions and Administration

To prepare pharmaceutical or sterile compositions of the anti-ILT3, anti-ILT3 ligand (e.g., anti-PI16) and anti-ILT3/ILT3 ligand (e.g., anti-ILT3/PI16) antibodies (e.g., humanized antibodies such as antagonist humanized antibodies) and antigen-binding fragments thereof, the antibody or antigen-binding fragment thereof is admixed with a pharmaceutically acceptable carrier or excipient. See, e.g., Remington's Pharmaceutical Sciences and U.S. Pharmacopeia: National Formulary, Mack Publishing Company, Easton, Pa. (1984). Such compositions are part of the present invention.

The scope of the present invention includes dessicated, e.g., freeze-dried, compositions comprising an anti-ILT3, anti-ILT3 ligand (e.g., anti-PI16) and anti-ILT3/ILT3 ligand (e.g., anti-ILT3/PI16) antibody or antigen-binding fragment thereof or a pharmaceutical composition thereof that includes a pharmaceutically acceptable carrier but substantially lacks water.

Formulations of therapeutic and diagnostic agents may be prepared by mixing with acceptable carriers, excipients, or stabilizers in the form of, e.g., lyophilized powders, slurries, aqueous solutions or suspensions (see, e.g., Hardman, et al. (2001) Goodman and Gilman's The Pharmacological Basis of Therapeutics, McGraw-Hill, New York, NY; Gennaro (2000) Remington: The Science and Practice of Pharmacy, Lippincott, Williams, and Wilkins, New York, N.Y.; Avis, et al. (eds.) (1993) Pharmaceutical Dosage Forms: Parenteral Medications, Marcel Dekker, N.Y.; Lieberman, et al. (eds.) (1990) Pharmaceutical Dosage Forms: Tablets, Marcel Dekker, N.Y.; Lieberman, et al. (eds.) (1990) Pharmaceutical Dosage Forms: Disperse Systems, Marcel Dekker, N.Y.; Weiner and Kotkoskie (2000) Excipient Toxicity and Safety, Marcel Dekker, Inc., New York, N.Y.).

Toxicity and therapeutic efficacy of the antibody or fragment compositions, administered alone or in combination with another therapeutic agent, can be determined by standard pharmaceutical procedures in cell cultures or experimental animals, e.g., for determining the LD₅₀ (the dose lethal to 50% of the population) and the ED₅₀ (the dose effective in 50% of the population). The dose ratio between toxic and therapeutic effects is the therapeutic index (LD₅₀/ED₅₀). In particular aspects, antibodies exhibiting high therapeutic indices are desirable. The data obtained from these cell culture assays and animal studies can be used in formulating a range of dosage for use in human. The dosage of such compounds lies preferably within a range of circulating concentrations that include the ED₅₀ with little or no toxicity. The dosage may vary within this range depending upon the dosage form employed and the route of administration.

In a further embodiment, a further therapeutic agent that is administered to a subject in association with an anti-ILT3, anti-ILT3 ligand (e.g., anti-PI16) and anti-ILT3/ILT3 ligand (e.g., anti-ILT3/PI16) (e.g., humanized antibody such as antagonist humanized antibodies) or antigen-binding fragment thereof disclosed herein is administered to the subject in accordance with the Physicians' Desk Reference 2003 (Thomson Healthcare; 57th edition (Nov. 1, 2002)).

The mode of administration can vary. Routes of administration include oral, rectal, transmucosal, intestinal, parenteral; intramuscular, subcutaneous, intradermal, intramedullary, intrathecal, direct intraventricular, intravenous, intraperitoneal, intranasal, intraocular, inhalation, insufflation, topical, cutaneous, transdermal, or intra-arterial.

The present invention provided methods for administering an anti-ILT3, anti-ILT3 ligand (e.g., anti-PI16) and anti-ILT3/ILT3 ligand (e.g., anti-ILT3/PI16) antibody or antigen-binding fragment thereof comprising introducing the antibody or fragment into the body of a subject. For example, the method comprises piercing the body of the subject with a needle of a syringe and injecting the antibody or fragment into the body of the subject, e.g., into the vein, artery, tumor, muscular tissue or subcutis of the subject.

The present invention provides a vessel (e.g., a plastic or glass vial, e.g., with a cap or a chromatography column, hollow bore needle or a syringe cylinder) comprising any of the antibodies or antigen-binding fragments, polypeptides or polynucleotides set forth herein or a pharmaceutical composition thereof comprising a pharmaceutically acceptable carrier.

The present invention also provides an injection device comprising any of the antibodies or antigen-binding fragments set forth herein or a pharmaceutical composition thereof. An injection device is a device that introduces a substance into the body of a patient via a parenteral route, e.g., intramuscular, subcutaneous or intravenous. For example, an injection device may be a syringe (e.g., pre-filled with the pharmaceutical composition, such as an auto-injector) which, for example, includes a cylinder or barrel for holding fluid to be injected (e.g., comprising the antibody or fragment or a pharmaceutical composition thereof), a needle for piecing skin and/or blood vessels for injection of the fluid; and a plunger for pushing the fluid out of the cylinder and through the needle bore. In an embodiment of the invention, an injection device that comprises an antibody or antigen-binding fragment thereof of the present invention or a pharmaceutical composition thereof is an intravenous (IV) injection device. Such a device includes the antibody or fragment or a pharmaceutical composition thereof in a cannula or trocar/needle which may be attached to a tube which may be attached to a bag or reservoir for holding fluid (e.g., saline; or lactated ringer solution comprising NaCl, sodium lactate, KCl, CaCl₂ and optionally including glucose) introduced into the body of the patient through the cannula or trocar/needle. The antibody or fragment or a pharmaceutical composition thereof may, in an embodiment of the invention, be introduced into the device once the trocar and cannula are inserted into the vein of a subject and the trocar is removed from the inserted cannula. The IV device may, for example, be inserted into a peripheral vein (e.g., in the hand or arm); the superior vena cava or inferior vena cava, or within the right atrium of the heart (e.g., a central IV); or into a subclavian, internal jugular, or a femoral vein and, for example, advanced toward the heart until it reaches the superior vena cava or right atrium (e.g., a central venous line). In an embodiment of the invention, an injection device is an autoinjector; a jet injector or an external infusion pump. A jet injector uses a high-pressure narrow jet of liquid which penetrate the epidermis to introduce the antibody or fragment or a pharmaceutical composition thereof to a patient's body. External infusion pumps are medical devices that deliver the antibody or fragment or a pharmaceutical composition thereof into a patient's body in controlled amounts. External infusion pumps may be powered electrically or mechanically. Different pumps operate in different ways, for example, a syringe pump holds fluid in the reservoir of a syringe, and a moveable piston controls fluid delivery, an elastomeric pump holds fluid in a stretchable balloon reservoir, and pressure from the elastic walls of the balloon drives fluid delivery. In a peristaltic pump, a set of rollers pinches down on a length of flexible tubing, pushing fluid forward. In a multi-channel pump, fluids can be delivered from multiple reservoirs at multiple rates.

The pharmaceutical compositions disclosed herein may also be administered with a needleless hypodermic injection device; such as the devices disclosed in U.S. Pat. Nos. 6,620,135; 6,096,002; 5,399,163; 5,383,851; 5,312,335; 5,064,413; 4,941,880; 4,790,824 or 4,596,556. Such needleless devices comprising the pharmaceutical composition are also part of the present invention. The pharmaceutical compositions disclosed herein may also be administered by infusion. Examples of well-known implants and modules for administering the pharmaceutical compositions include those disclosed in: U.S. Pat. No. 4,487,603, which discloses an implantable micro-infusion pump for dispensing medication at a controlled rate; U.S. Pat. No. 4,447,233, which discloses a medication infusion pump for delivering medication at a precise infusion rate; U.S. Pat. No. 4,447,224, which discloses a variable flow implantable infusion apparatus for continuous drug delivery; U.S. Pat. No. 4,439,196, which discloses an osmotic drug delivery system having multi-chamber compartments. Many other such implants, delivery systems, and modules are well known to those skilled in the art and those comprising the pharmaceutical compositions of the present invention are within the scope of the present invention.

Alternately, one may administer the anti-ILT3, anti-ILT3 ligand (e.g., anti-PI16) and anti-ILT3/ILT3 ligand (e.g., anti-ILT3/PI16) antibody (e.g., humanized antibody such as antagonist humanized antibodies) or antigen-binding fragment in a local rather than systemic manner, for example, via injection of the antibody or fragment directly into a tumor. Furthermore, one may administer the antibody or fragment in a targeted drug delivery system, for example, in a liposome coated with a tissue-specific antibody, targeting, for example, a tumor. The liposomes will be targeted to and taken up selectively by the afflicted tissue. Such methods and liposomes are part of the present invention.

“Treat” or “treating” means to administer anti-ILT3, anti-ILT3 ligand (e.g., anti-PI16) and anti-ILT3/ILT3 ligand (e.g., anti-ILT3/PI16) antibodies or antigen-binding fragments thereof of the present invention, to a subject having one or more symptoms of a disease for which the antibodies and antigen-binding fragments are effective, e.g., in the treatment of a subject having cancer or an infectious disease, or being suspected of having cancer or infectious disease, for which the agent has therapeutic activity. Typically, the antibody or fragment is administered in an “effective amount” or “effective dose” which will alleviate one or more symptoms (e.g., of cancer or infectious disease) in the treated subject or population, whether by inducing the regression or elimination of such symptoms or by inhibiting the progression of such symptom(s), e.g., cancer symptoms such as tumor growth or metastasis, by any clinically measurable degree. The effective amount of the antibody or fragment may vary according to factors such as the disease stage, age, and weight of the patient, and the ability of the drug to elicit a desired response in the subject.

Determination of the appropriate dose is made by the clinician, e.g., using parameters or factors known or suspected in the art to affect treatment. Generally, in determining the dose, the dose begins with an amount somewhat less than the optimum dose and it is increased by small increments thereafter until the desired or optimum effect is achieved relative to any negative side effects. Important diagnostic measures include those of symptoms of, e.g., the inflammation or level of inflammatory cytokines produced. In general, it is desirable that a biologic that will be used is derived from the same species as the animal targeted for treatment, thereby minimizing any immune response to the reagent. In the case of human subjects, for example, chimeric, humanized and fully human antibodies are may be desirable. Guidance in selecting appropriate doses of anti-LAG3 antibodies or fragments is available (see, e.g., Wawrzynczak (1996) Antibody Therapy, Bios Scientific Pub. Ltd, Oxfordshire, UK; Kresina (ed.) (1991) Monoclonal Antibodies, Cytokines and Arthritis, Marcel Dekker, New York, N.Y.; Bach (ed.) (1993) Monoclonal Antibodies and Peptide Therapy in Autoimmune Diseases, Marcel Dekker, New York, N.Y.; Baert et al. (2003) New Engl. J. Med. 348:601-608; Milgrom et al. (1999) New Engl. J. Med. 341:1966-1973; Slamon et al. (2001) New Engl. J. Med. 344:783-792; Beniaminovitz et al. (2000) New Engl. J. Med. 342:613-619; Ghosh et al. (2003) New Engl. J. Med. 348:24-32; Lipsky et al. (2000) New Engl. J. Med. 343:1594-1602).

Whether a disease symptom has been alleviated can be assessed by any clinical measurement typically used by physicians or other skilled healthcare providers to assess the severity or progression status of that symptom. While an embodiment of the present invention (e.g., a treatment method or article of manufacture) may not be effective in alleviating the target disease symptom(s) in every subject, it should alleviate the target disease symptom(s) in a statistically significant number of subjects as determined by any statistical test known in the art such as the Student's t-test, the chi²-test, the U-test according to Mann and Whitney, the Kruskal-Wallis test (H-test), Jonckheere-Terpstra-test and the Wilcoxon-test.

Further provided are methods for treating or preventing cancer in subjects, such as human subjects, in need of such treatment by administering an effective amount of the anti-ILT3, anti-ILT3 ligand (e.g., anti-PI16) and anti-ILT3/ILT3 ligand (e.g., anti-ILT3/PI16) antibodies or antigen-binding fragments thereof of the present invention which are disclosed herein which may be effective for such treatment or prevention. In an embodiment of the invention, such a subject suffers from and is treated for cancer, e.g., a solid tumor which includes, in addition to the tumor cells, tumor infiltrating lymphocytes (TILs), such as T-cells, expressing LAG3.

The present invention also provides methods for treating or preventing an infectious disease in a subject by administering an effective amount of anti-ILT3, anti-ILT3 ligand (e.g., anti-PI16) and anti-ILT3/ILT3 ligand (e.g., anti-ILT3/PI16) antibodies or antigen-binding fragments thereof disclosed herein to the subject which may be effective for such treatment or prevention. In an embodiment of the invention, the infectious disease is viral infection. In an embodiment of the invention, the infectious disease is bacterial infection. In an embodiment of the invention, the infectious disease is parasitic infection. In an embodiment of the invention, the infectious disease is fungal infection.

EXAMPLES

These examples are intended to exemplify the present invention are not a limitation thereof. Compositions and methods set forth in the Examples form part of the present invention. 0

Example 1 Discovery of ILT3 Ligand

Cell microarray technology was used to identify specific binding partners for an ILT3Fc-fusion protein. PI16 was discovered to be an ILT3 binding partner. See FIG. 1. Background binding tests showed dose-dependent levels of background binding of the test ligand to untransfected HEK293 cells. Based upon this, 10 μg/mL of the test protein was selected for the binding screen against 3559 human plasma membrane proteins, each individually expressed in human HEK293 cells. This revealed 42 primary hits, many of which were of weak or very weak intensity. Each primary hit was re-expressed and tested with the test ligand and controls. A positive control ligand: receptor interaction (CTLA4-hFc:CD86) was used to confirm the screening and detection conditions. The confirmation screen yield six potential hits, including NIPA1 (non-imprinted in Prader-Willi/Angelman syndrome 1), PODXL2 (Podocalyxin-Like 2), MAG (Myelin Associated Glycoprotein), VSIG1 (V-set and immunoglobulin domain containing 1), PI16 (Peptidase inhibitor 16), and CLDN3 (Claudin3).

Hits were validated by transient expression of cDNA vectors on HEK293T (human embryonic kidney) cells and co-cultured with an ILT3 signaling reporter cell line. See FIG. 2. FcγR2B vector transfected cells served as a control. An ILT3 reporter cell line was constructed by linking the extracellular domains of ILT3 with the intracellular signaling domain of CD3z chain (ILT3-fusion protein). The reporter cells also contained an NFAT transcription factor-dependent luciferase gene sequence. Upon ILT3-CD3z co-ligation, NFAT signaling led to transcription and production of luciferase. It was shown that PI16 expressing cells promoted a 2 log increase in luciferase activity of ILT3 reporter cells suggesting that PI16 expressed on the 293T cells were able to “co-ligate” ILT3 and drive CD3z-NFAT-Luciferase activity. In contrast, none of the other expression vectors including FcyR2B vectors induced any luciferase activities. See FIG. 3.

PI16 is expressed by a subset of human memory Treg with enhanced migration to CCL17 and CCL20. It was shown by microarray analysis to be over-expressed by CD4-positive/CD25-positive Treg compared with CD4-positive/CD25-negative Th cells. However, while PI16 serves as a marker for a small subset of inflammatory tissue infiltrating Treg cells, there has been no known function for PI16 on lymphocytes. (Cell Immunol. 2012 January-Febuary;275(1-2):12-8). As shown in FIG. 4, PI16 has 3 isoforms, including a long form with C-terminal GPI anchor sequence, a short splice variant with deletion of 232 to 424 amino acids but retaining the C-terminal anchor sequence (270 amino acids), and finally, a nearly full length form that lacks the C-terminal anchor sequence.

To directly demonstrate the PI16 interaction with ILT3, PI16 was transfected into 3A9 cells and ILT3Fc alone or ILT3Fc crosslinked with a goat anti-human IgG Fc gamma specific antibody were used to stain the PI16 positive cells as illustrated in FIG. 5. ILT3Fc has the amino acid sequence set forth in SEQ ID NO:47, which shows the mature ILT3Fc protein. ILT3Fc alone stained PI16 transfectins (8.3%). ILT3Fc complex showed enhanced staining to PI16⁺ cells (23%). ILT3Fc was titrated from 10 μg/mL to 0.16 μg/mL with 2.5 to 5 μg/mL yielding the best staining. Mouse VISTA-Fc was used as an irrelevant staining control and the parental 3A9 cells transfected with control vector do not bind ILT3Fc. The data clearly showed that ILT3Fc can directly bind PI16 expressed on cell surface. See FIG. 6.

Example 2 Production of Anti-ILT3 Antibodies

Antibodies that bind specifically to ILT3 were made and characterized.

Antibody isolation. Six- to eight-week-old female Balb/c mice (Taconic Biosci.) were immunized in the right hind leg footpad with 5 μg of ILT3 (amino acid #22-259, GenBank: ABM86208.1) human IgG1 fusion protein (CH2 and CH3 of hIgG1) in PBS mixed with Sigma Adjuvant System (Sigma cat# 56322-1VL) at a 1:1 ratio (v/v). The first 6 doses of human ILT3Fc protein were administered every 3 to 4 days. The last 4 doses were given once every week. Mice were sacrificed 3 days later and cells were isolated from draining inguinal lymph node.

Lymphocytes were fused by electrofusion to a mouse myeloma cell line, P3X (ATCC), based upon standard protocols. Cells were plated at approximately 2×10⁵ cells/mL in a flat bottom microtiter plate, followed by a two week incubation in DMEM/F12 selective hybridoma medium containing 15% Fetal Bovine Serum, 1 ng/mL recombinant murine IL-6 (R&D), 1× Penicillin-Streptomycin-Glutamine (Life Technologies), 1 mM sodium pyruvate (Life Technologies), 1% OPI Media Supplement (Sigma) and 1× HAT (Sigma). After two weeks, cells were cultured in medium in which the HAT is replaced with HT (Sigma). The resulting hybridomas were then screened for the production of ILT3-specific antibodies.

Supernatants from individual wells were first screened by ELISA for anti-ILT3 monoclonal IgG antibodies. Nunc MaxiSorp flat-bottom 96-well plates (Thermo Scientific) were coated overnight at 4° C. with either 1 μg/mL human ILT3Fc or human IgG1 control. After washing with PBS+0.05% Tween 20 for 3 times, 50 μL of hybridoma supernatant was added to the wells. After 2 hours of incubation at 37° C., plates were washed and 50 μL of 1:4000 HRP-conjugated goat anti-mouse IgG antibody (Southern Biotech cat# 1043-05) was added to the wells, followed by 2 hours of incubation at 37° C. 100 μL of TMB substrate (Pierce) were added to the wells after washing. Reaction was developed after 10 to 15 minutes and stopped by 100 μL of 0.16 M sulfuric acid (Life technologies). Plates were read at 450 nm absorbance. From the primary screening, 239 wells were selected for secondary screening based on absorbance reading greater than 0.7 for ILT3Fc (less than 50% positivity for corresponding IgG1 control).

Secondary screening was performed on human monocytes from PBMCs by flow cytometry. Human monocytes were reported to express a high level of ILT3 and the result was confirmed by staining the cells with commercially available ILT3 antibody eBioscience, clone ZM4.1). Before staining, cells were pre-incubated with 0.2 μg of goat IgG to block human Fc receptors for 15 minutes at 4° C. Then 80 μL of the hybridoma supernatants was added to each well and incubated for 30 mins at 4° C. After washing the cells, PE-conjugated goat anti-mouse IgG was added to detect the presence of the ILT3 antibodies. Stained cells were analyzed by FACS LSR. Negative population was defined by adding PE-conjugated goat anti-mouse IgG to the cells without the hybridoma supernatants; there was no signal in the PE channel. Positive wells were expanded in preparation for cloning.

Expanded wells were screened again on human monocytes by flow cytometry as illustrated above. Cells from positive wells were diluted to 3 cells/mL and 100 μL aliquots were plated in each well for a total of five flat-bottom 96-well plates. After two weeks, supernatants were collected and screened by flow cytometry on THP-1 cells, a human monocyte cell line that has been reported to express high level of ILT3 and the result was confirmed by staining the cells with commercially available ILT3 antibody (eBioscience, clone ZM4.1).

Binding affinity. The Pall ForteBio Octet instrument uses disposable fiber-optic sensors that detect biomolecular interactions using a proprietary biolayer interferometry. It is a dip-and-read system where ligand-coated sensor tips are immersed in analyte-containing wells of a microplate. The Octet can be used to run epitope binning assays for the characterization of antibodies. One binning assay format is the tandem assay where the antigen is immobilized onto a biosensor and then presented to the two competing antibodies in consecutive steps. Binding to distinct non-overlapping epitopes is indicated if saturation with the first antibody (Ab1) does not block binding of the second antibody (Ab2). Antibodies are tested in a pair-wise combinatorial manner and those which compete for the same binding site are grouped into the same bin.

Instrument. Octet QK384

Anti ILT3 antibody samples. Antibodies were provided as hybridoma supernatants with estimated antibody concentrations (determined by Octet quantitation methods).

Binding assay. Anti-ILT3 antibodies were first tested to ensure binding to human ILT3/human IgG. The running buffers for testing antibody supernatants were production medium and 1× Kinetics Buffer (diluted from 10X Kinetics Buffer, ForteBio Cat# 18-5032), respectively. Anti-human Fc (AHC) biosensors (ForteBio Cat# 18-5060) were pre-wet for 5 minutes in running buffer then dipped into same (60 s) to establish a baseline. Human ILT3/human IgG (40 nM, 600 s) was immobilized on the tips, then dipped into the anti-ILT3 antibody (167 nM, 600 s), and finally immersed back into running buffer to observe dissociation (300 s) of antibody from ligand.

Binning assay. Anti-ILT3 antibodies were binned by tandem assay. Anti-human Fc (AHC) biosensors (ForteBio Cat# 18-5060) were pre-wet for 5 minutes in running buffer (refer to Binding Assay) then dipped into same (60 s) to establish a baseline. Human ILT3/human IgG (40 nM, 600 s) was immobilized on the tips and then dipped into the first antibody (167 nM, 300 or 600 s) followed by the second antibody (167 nM, 120 s).

Binning analysis. Binning results were analyzed using the epitope binning features available in ForteBio Octet Data Analysis software v8.0. Two-dimensional matrices are generated to analyze the pair-wise combinations for blocking status. In the matrices, the rows represent Ab1 and the columns represent competing Ab2. A cell represents an antibody pair and is color-coded by its blocking status where one color designates blocked pairs and another color designates non-blocking pairs. This aids to summarize antibodies into appropriate epitope bins.

Cross-competition assay to determine epitope similarity. To determine whether the anti-ILT3 antibodies recognized similar epitope, a two-step binding assay was performed. The biosensor with immobilized ILT3Fc picked up the first antibody and then was dipped into the various secondary antibodies. If the epitope of the second antibody was similar to the first antibody, then there was no additional signal. If the epitope of the second antibody was different than the first antibody, additional signal was recorded since the second antibody can still bind to the exposed epitope not bound by the first antibody. Overall, Octet data demonstrated that DX435, DX439 and DX440 fell into one bin while DX446 fell into another.

Example 3 Identification of Anti-ILT3 Antibodies that Block PI16 Binding and Function

The capacity of anti-ILT3 antibodies—identified in Example 2—to inhibit PI16 binding was tested. In general, there were 3 bins for the way anti-ILT3 antibodies interacted with PI16. Some of the antibodies did not affect ILT3 binding to PI16 (e.g., 11G3, 31G11, which have similar binding as isotype control mAbs). Some antibodies were partial blockers (e.g., Ab1 and Ab2, which have lower binding compared to isotype controls). Finally, there were three unique antibodies that completely blocked ILT3 binding to PI16 (Ab3-5).

Example 4 Treatment of Tumor-Bearing CD34 Humanized Mice with Anti-ILT3 Antibody

CD34 humanized mice (NSG mice, The Jackson Laboratory) were injected subcutaneously on the left flank with 1.5×10⁶ SKMELS tumor cells, a melanoma cell line obtained from ATCC. Intraperitoneal treatment of either isotype (mouse IgG1K) or test antibodies at 50 mpk (mg per kg) was given when tumor size reached 100-130 mm³. Second treatment dose was given 7 days after the initial dose. Each experimental group consisted of 4 animals. Tumor growth was recorded every 7 days. Once treatment started, tumor growth was recorded every 4 days. Mice were sacrificed 7 days after the second treatment dose.

A phenotypical profile of human CD11b+ myeloid cells in spleen and tumor from SKMELS tumor bearing mouse is set forth in FIG. 8. Proportions of ILT3+and ILT11+ CD11b+ myeloid cells were determined. Results showed that ILT3 (ITIM containing inhibitory receptor) and ILT11 (associates with ITAM activating receptor) are expressed on a different subsets of CD11b+ myeloid cells. These two subsets of immune cells may have distinct function based on their expression of an immune inhibitory versus activation receptors.

Anti-ILT3 (DX446) treatment led to tumor growth inhibition. Tumor growth was measured in CD34 humanized mice transplanted with SKMEL5 and treated with either isotype (n=4, grey circle) or DX446 (n=4, black circle) at 50 mpk. Two out of the 4 tumors in the DX446 treated groups regressed (See FIG. 9). Results are representative of 3 separate experiments. Error bars represent SEM.

To determine whether the effect of tumor inhibition correlated with a switch in myeloid cell phenotype, we isolated splenocytes and compared ILT3, ILT11, and CD33 expression. After anti-ILT3 (DX446) treatment, there was a significant increase in ILT11-expressing myeloid cells along with a decrease in ILT3 and CD33-expressing cells (see FIG. 10). ILT11 is associated with immunoreceptor tyrosine-based activation motif (ITAM) and promotes activating signals to myeloid cells. In contrast, both ILT3 and CD33 contain immunoreceptor tyrosine-based inhibition motifs (ITIM) and are suppressive. Therefore after anti-ILT3 treatment, the myeloid cell compartment skewed toward a proinflammatory phenotype.

Example 5 Anti-PD1 Activated T Cells have Enhanced PI16 Expression

Humanized mice (CD34+ hematopoietic stem cells engrafted NSG mice) transplanted with PANC08 human pancreatic tumor cells were treated with isotype control antibody or anti-PD1 antibody, Pembrolizumab. Spleen cells were isolated, stained with CD3, CD4, CD8 and anti-PI16, and analyzed by flow cytometry. As shown in FIG. 11, PI16+ CD3+ CD8+ cells have lower level of TIGIT (T cell exhaustion marker) and higher level of Granzyme B (cytotoxic marker) compared to PI16 negative cells. This result indicates that PI16 is expressed on a population of activated T cells and that anti-PD1 treatment enhanced PI16 expression.

Example 6 Identification of Anti-PI16 Antibodies that Blocked ILT3Fc Binding

Nine antibodies were identified to bind CHO cells expressing cell surface recombinant PI16 (FIG. 12, top panel). The heavy chain and light chain variable domain of anti-PI16 antibodies 20B5, 49A7, 10E3, and 32A4 were sequenced.

SEQ ID NO: Heavy chain Light chain variable varaible Antibody domain domain 20B5 48 49 49A7 50 51 10E3 52 53 32A4 54 55 Five of the anti-PI16 antibodies blocked ILT3Fc binding. 3A9 cells were transfected with a cDNA vector encoding human PI16 and were subjected to staining with ILT3Fc. Goat anti-human Fc was used as a secondary staining antibody. Anti-PI16 Clones 20B5, 44A5, 10E3, 49A7, and 20G8 blocked PI16+cell binding to ILT3Fc. These antibody clones engage critical contact residues between PI16 and ILT3. As shown in FIG. 12, clones 34A1, 10H9, and 48A4 did not block PI16+cell binding to ILT3Fc, indicating that 34A1, 10H9, and 48A4 engage PI16 epitope(s) not relevant for binding to ILT3.

Example 7 Plate Bound Recombinant PI16 Down-Regulates Dendritic Cell Activation Which is Reversible by PI16 Antagonist Antibodies (49A7 and 10E3)

Healthy human donor CD14+monocytes were differentiated in GMCSF and IL4 for 6 days and stimulated with IFNα and LPS 24 hours prior to the assay. PI16 bound to 96 well plate was incubated with control antibody or PI16 antibodies for 30 minutes, washed, and activated dendritic cells were added. Following 72 hours stimulation, cells were analyzed for CD86 expression and cytokine production.

As shown in FIG. 13, clones 49A7 and 10E3 blocked recombinant PI16 activation of human PBMC. Clone 34A1, which is a non-ILT3-blocker did not inhibit activation of human monocytes. This result is consistent with the concept that PI16 expressed by activated T cells serves as a feedback inhibitor to limit activation of ILT330 myeloid cells. Therefore, by targeting this molecular pathway, the immune system can be turned-up to enhance reactivity for cancer immunotherapy.

Table of Antibody Sequences SEQ ID NO DESCRIPTION SEQUENCE  1 Human ILT3 precursor with MIPTFTALLCLGLSLGPRTHM QAGPLPKPTLWAE 21 amino acid signal PGSVISWGNSVTIWCQGTLEAREYRLDKEESPAP sequence; WDRQNPLEPKNKARFSIPSMTEDYAGRYRCYYRS Amino acids 22-259 PVGWSQPSDPLELVMTGAYSKPTLSALPSPLVTS extracellular domain GKSVTLLCQSRSPMDTFLLIKERAAHPLLHLRSE HGAQQHQAEFPMSPVTSVHGGTYRCFSSHGFSHY LLSHPSDPLELIVSGSLEDPRPSPTRSVSTAAGP EDQPLMPTGSVPHSGLRRHWEVLIGVLVVSILLL SLLLFLLLQHWRQGKHRTLAQRQADFQRPPGAAE PEPKDGGLQRRSSPAADVQGENFCAAVKNTQPED GVEMDTRQSPHDEDPQAVTYAKVKHSRPRREMAS PPSPLSGEFLDTKDRQAEEDRQMDTEAAASEAPQ DVTYAQLHSFTLRQKATEPPPSQEGASPAEPSVY ATLAIH  2 Human PI16 long isoform MHGSCSFLMLLLPLLLLLVATTGPVGALTDEEKR precursor with 27 amino acid LMVELHNLYRAQVSPTASDMLHMRWDEELAAFAK signal sequence AYARQCVWGHNKERGRRGENLFAITDEGMDVPLA MEEWHHEREHYNLSAATCSPGQMCGHYTQVVWAK TERIGCGSHFCEKLQGVEETNIELLVCNYEPPGN VKGKRPYQEGTPCSQCPSGYHCKNSLCEPIGSPE DAQDLPYLVTEAPSFRATEASDSRKMGTPSSLAT GIPAFLVTEVSGSLATKALPAVETQAPTSLATKD PPSMATEAPPCVTTEVPSILAAHSLPSLDEEPVT FPKSTHVPIPKSADKVTDKTKVPSRSPENSLDPK MSLTGARELLPHAQEEAEAEAELPPSSEVLASVF PAQDKPGELQATLDHTGHTSSKSLPNFPNTSATA NATGGRALALQSSLPGAEGPDKPSVVSGLNSGPG HVWGPLLGLLLLPPLVLAGIF  3 Human PI16 short isoform MHGSCSFLMLLLPLLLLLVATTGPVGALTDEEKR precursor with 27 amino acid LMVELHNLYRAQVSPTASDMLHMRWDEELAAFAK signal sequence (lacks AYARQCVWGHNKERGRRGENLFAITDEGMDVPLA MEEWHHEREHYNLSAATCSPGQMCGHYTQVVWAK TERIGCGSHFCEKLQGVEETNIELLVCNYEPPGN VKGKRPYQEGTPCSQCPSGYHCKNSLCEPIGSPE DAQDLPYLVTEAPSFRATEASDSRKMGAEGPDKP SVVSGLNSGPGHVWGPLLGLLLLPPLVLAGIF  4 Human PI16 full-length MHGSCSFLMLLLPLLLLLVATTGPVGALTDEEKR secreted isoform precursor LMVELHNLYRAQVSPTASDMLHMRWDEELAAFAK with 27 amino acid signal AYARQCVWGHNKERGRRGENLFAITDEGMDVPLA sequence (Retrogenix) MEEWHHEREHYNLSAATCSPGQMCGHYTQVVWAK TERIGCGSHFCEKLQGVEETNIELLVCNYEPPGN VKGKRPYQEGTPCSQCPSGYHCKNSLCEPIGSPE DAQDLPYLVTEAPSFRATEASDSRKMGTPSSLAT GIPAFLVTEVSGSLATKALPAVETQAPTSLATKD PPSMATEAPPCVTTEVPSILAAHSLPSLDEEPVT FPKSTHVPIPKSADKVTDKTKVPSRSPENSLDPK MSLTGARELLPHAQEEAEAEAELPPSSEVLASVF PAQDKPGELQATLDHTGHTSSKSLPKFPQYLCHR  5 FLAG Tag DYKDDDDK  6 Human ILT11 (also known as MAPWSHPSAQLQPVGGDAVSPALMVLLCLGLSLG LILRA5 PRTHVQAGNLSKATLWAEPGSVISRGNSVTIRCQ GTLEAQEYRLVKEGSPEPWDTQNPLEPKNKARFS IPSMTEHHAGRYRCYYYSPAGWSEPSDPLELVVT GFYNKPTLSALPSPVVTSGENVTLQCGSRLRFDR FILTEEGDHKLSWTLDSQLTPSGQFQALFPVGPV TPSHRWMLRCYGSRRHILQVWSEPSDLLEIPVSG AADNLSPSQNKSDSGTASHLQDYAVENLIRMGMA GLILVVLGILIFQDWHSQRSPQAAAGR  7 Human ILT8 (also known as MTPTLAALLCLGLSLGPRTHVQAGPFPKPTLWAE LILRA6) PGSVISWGSPVTIWCQGSLEAQEYRLDKEGSPEP WDRNNPLEPKNKARFSIPSITEHHAGRYRCHYYS SAGWSEPSDPLELVMTGAYSKPTLSALPSPVVAS GGNMTLQCGSQKGYHHFVLMKEGEHQLPRTLDSQ QLHSGGFQALFPVGPVNPSHRWRFTCYYYYMNTP RVWSHPSDPLEILPSGVSRKPSLLTLQGPVLAPG QSLTLQCGSDVGYDRFVLYKEGERDFLQRPGQQP QAGLSQANFTLGPVSPSHGGQYRCYGAHNLSSEW SAPSDPLNILMAGQIYDTVSLSAQPGPTVASGEN VTLLCQSWWQFDTFLLTKEGAAHPPLRLRSMYGA HKYQAEFPMSPVTSAHAGTYRCYGSYSSNPHLLS FPSEPLELMVSGHSGGSSLPPTGPPSTPASHAKD YTVENLIRMGMAGLVLVFLGILLFEAQHSQRNPQ DAAGR  8 VH_DX446 QIQLVQSGPELKKPGETVKISCKASGYTFTNYRM TWVKQAPGKGLKWMGWINTNTGDPTYAEELKGRF AFSSETSASTAYLQINNLKNEDTATYFCAREGFF NYAMDYWGQGTSVTVSS  9 VL_DX446 DILLTQSPAILSVSPGKRVSFSCRASQSIGTSIH WYQQRTNGSPRLLIKYASESISGIPSRFSGSGSG TDFTLSINSVESEDIADYYCQQSNSWPPTFGAGT KLELK 10 VH_DX446 CDR1 NYRMT 11 VH_DX446 CDR2 WINTNTGDPTYAEELKG 12 VH_DX446 CDR3 EGFFNYAMDY 13 VL_DX446 CDR1 RASQSIGTSIH 14 VL_DX446 CDR2 YASESIS 15 VL_DX446 CDR3 QQSNSWPPT 16 VH_DX435 EVQLQQSGPEMVKPGASVKISCKASGYAFTDYNI HWVKKSHGKSPEWIGHIYPYNKDTVFNQNKTKAT LTVDKSTTTAYMDLRSLTSEDSAVYYCARGAVGY FDYWGQGTTLTVSS 17 VL_DX435 DIQMTQSPASLSASVGETVTITCRASGNIHNFLA WYQQKQGKSPQLLVYNAKTLADGVPSRFSGSGSG TQYSLKINSLQPEDFGSYYCQHFWSYPFTFGAGT KLELK 18 VH_DX435 CDR1 DYNIH 19 VH_DX435 CDR2 HIYPYNKDTVFNQNKT 20 VH_DX435 CDR3 GAVGYFDY 21 VL_DX435 CDR1 RASGNIHNFLA 22 VL_DX435 CDR2 NAKTLAD 23 VL_DX435 CDR3 QHFWSYPFT 24 VH_DX439 EVQLQQPGPELVKPGASVKISCKASGYTFTDYNM HWVRQRHGKSLEWIGHIYPYNGNTVYNQRFKNKA TLNVDNFSSTAYMELRSLTSEDSAVYYCARGAVG YFDHWGQGTTLTVSS 25 VL_DX439 DIQMTQSPASLSASVGETVTITCRASGNIHNFLA WYQQKQGRSPQLLVYNAKTLADGVPSRFSGSGSG TQYSLKINSLQPEDFGNYYCQHFWSYPFTFGAGT NLELK 26 VH_DX439 CDR1 DYNMH 27 VH_DX439 CDR2 HIYPYNGNTVYNQRFKN 28 VH_DX439 CDR3 GAVGYFDH 29 VL_DX439 CDR1 RASGNIHNFLA 30 VL_DX439 CDR2 NAKTLAD 31 VL_DX439 CDR3 QHFWSYPFT 32 VH_DX440 EVQLQQSGPELVKPGASVKISCKASGYTFSDYNM HWVKQSHGKSLKWIGHIFPYIGDTVYNQKFTSKA TLTVDNSSSTGYMEIRSLTSEDSAVYYCARGAVG YFDYWGQGTTLTVSS 33 VL_DX440 DIQMTQSPASLSASVGETVTITCRASGNIHNYLA WYQQKQGKSPQFLVYNAKTLADGVPSRFSGSGSG TQYSLKINSLQPEDFGTYYCQHFWSFPFTFGAGT KLELK 34 VH_DX440 CDR1 DYNMH 35 VH_DX440 CDR2 HIFPYIGDTVYNQKFTS 36 VH_DX440 CDR3 GAVGYFDY 37 VL_DX440 CDR1 RASGNIHNYLA 38 VL_DX440 CDR2 NAKTLAD 39 VL_DX440 CDR3 QHFWSFPFT 41 Human ILT3 mature protein QAGPLPKPTLWAEPGSVISWGNSVTIWCQGTLEA Extracellular domain amino REYRLDKEESPAPWDRQNPLEPKNKARFSIPSMT acids 1-238 EDYAGRYRCYYRSPVGWSQPSDPLELVMTGAYSK PTLSALPSPLVTSGKSVTLLCQSRSPMDTFLLIK ERAAHPLLHLRSEHGAQQHQAEFPMSPVTSVHGG TYRCFSSHGFSHYLLSHPSDPLELIVSGSLEDPR PSPTRSVSTAAGPEDQPLMPTGSVPHSGLRRHWE VLIGVLVVSILLLSLLLFLLLQHWRQGKHRTLAQ RQADFQRPPGAAEPEPKDGGLQRRSSPAADVQGE NFCAAVKNTQPEDGVEMDTRQSPHDEDPQAVTYA KVKHSRPRREMASPPSPLSGEFLDTKDRQAEEDR QMDTEAAASEAPQDVTYAQLHSFTLRQKATEPPP SQEGASPAEPSVYATLAIH 42 Human PI6 long isoform LTDEEKRLMVELHNLYRAQVSPTASDMLHMRWDE mature protein ELAAFAKAYARQCVWGHNKERGRRGENLFAITDE GMDVPLAMEEWHHEREHYNLSAATCSPGQMCGHY TQVVWAKTERIGCGSHFCEKLQGVEETNIELLVC NYEPPGNVKGKRPYQEGTPCSQCPSGYHCKNSLC EPIGSPEDAQDLPYLVTEAPSFRATEASDSRKMG TPSSLATGIPAFLVTEVSGSLATKALPAVETQAP TSLATKDPPSMATEAPPCVTTEVPSILAAHSLPS LDEEPVTFPKSTHVPIPKSADKVTDKTKVPSRSP ENSLDPKMSLTGARELLPHAQEEAEAEAELPPSS EVLASVFPAQDKPGELQATLDHTGHTSSKSLPNF PNTSATANATGGRALALQSSLPGAEGPDKPSVVS GLNSGPGHVWGPLLGLLLLPPLVLAGIF 43 Human PI16 short isoform LTDEEKRLMVELHNLYRAQVSPTASDMLHMRWDE mature protein ELAAFAKAYARQCVWGHNKERGRRGENLFAITDE GMDVPLAMEEWHHEREHYNLSAATCSPGQMCGHY TQVVWAKTERIGCGSHFCEKLQGVEETNIELLVC NYEPPGNVKGKRPYQEGTPCSQCPSGYHCKNSLC EPIGSPEDAQDLPYLVTEAPSFRATEASDSRKMG AEGPDKPSVVSGLNSGPGHVWGPLLGLLLLPPLV LAGIF 44 Human PI16 full-length LTDEEKRLMVELHNLYRAQVSPTASDMLHMRWDE secreted isoform protein ELAAFAKAYARQCVWGHNKERGRRGENLFAITDE (Retrogenix) GMDVPLAMEEWHHEREHYNLSAATCSPGQMCGHY TQVVWAKTERIGCGSHFCEKLQGVEETNIELLVC NYEPPGNVKGKRPYQEGTPCSQCPSGYHCKNSLC EPIGSPEDAQDLPYLVTEAPSFRATEASDSRKMG TPSSLATGIPAFLVTEVSGSLATKALPAVETQAP TSLATKDPPSMATEAPPCVTTEVPSILAAHSLPS LDEEPVTFPKSTHVPIPKSADKVTDKTKVPSRSP ENSLDPKMSLTGARELLPHAQEEAEAEAELPPSS EVLASVFPAQDKPGELQATLDHTGHTSSKSLPKF PQYLCHR 45 Human ILT11 mature protein GNLSKATLWAEPGSVISRGNSVTIRCQGTLEAQE YRLVKEGSPEPWDTQNPLEPKNKARFSIPSMTEH HAGRYRCYYYSPAGWSEPSDPLELVVTGFYNKPT LSALPSPVVTSGENVTLQCGSRLRFDRFILTEEG DHKLSWTLDSQLTPSGQFQALFPVGPVTPSHRWM LRCYGSRRHILQVWSEPSDLLEIPVSGAADNLSP SQNKSDSGTASHLQDYAVENLIRMGMAGLILVVL GILIFQDWHSQRSPQAAAGR 46 Human ILT8 mature protein QAGPFPKPTLWAEPGSVISWGSPVTIWCQGSLEA QEYRLDKEGSPEPWDRNNPLEPKNKARFSIPSIT EHHAGRYRCHYYSSAGWSEPSDPLELVMTGAYSK PTLSALPSPVVASGGNMTLQCGSQKGYHHFVLMK EGEHQLPRTLDSQQLHSGGFQALFPVGPVNPSHR WRFTCYYYYMNTPRVWSHPSDPLEILPSGVSRKP SLLTLQGPVLAPGQSLTLQCGSDVGYDRFVLYKE GERDFLQRPGQQPQAGLSQANFTLGPVSPSHGGQ YRCYGAHNLSSEWSAPSDPLNILMAGQIYDTVSL SAQPGPTVASGENVTLLCQSWWQFDTFLLTKEGA AHPPLRLRSMYGAHKYQAEFPMSPVTSAHAGTYR CYGSYSSNPHLLSFPSEPLELMVSGHSGGSSLPP TGPPSTPASHAKDYTVENLIRMGMAGLVLVFLGI LLFEAQHSQRNPQDAAGR 47 ITL3Fc (extracellular domain QAGPLPKPTLWAEPGSVISWGNSVTIWCQGTLEA amino acids 1-238)(Fc amino REYRLDKEESPAPWDRQNPLEPKNKARFSIPSMT acids 239-463) EDYAGRYRCYYRSPVGWSQPSDPLELVMTGAYSK PTLSALPSPLVTSGKSVTLLCQSRSPMDTFLLIK ERAAHPLLHLRSEHGAQQHQAEFPMSPVTSVHGG TYRCFSSHGFSHYLLSHPSDPLELIVSGSLEGPR PSPTRSVSTAAGPEDQPLMPTGSVPHSGLRRHWE THTCPPCPAPELLGGPSVFLEPPKPKDTLMISRT PEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTK PREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVS NKALPAPIEKTISKAKGQPREPQVYTLPPSRDEL TKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYK TTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCS VMHEALHNHYTQKSLSLSPGK 48 Anti-PI16 clone 20B5 heavy EVQLLESGGGLVQPGGSLRVSCAASGFTFSSYAM chain variable domain SWVRQAPGKGLEWVSTISGSGGTTHYADSVKGRF TISRDNSKNTVYMQMSSLRAEDTAAYYCAKDLGL RAQGWFDPWGQGTLVTVSS 49 Anti-PI16 clone 20B5 light QLVLTQSPSASASLGASVKLTCTLSSGHSSYAIA chain variable domain WHQQQPEKGPRYLMKLNSDGSHSKGDGIPDRFSG SSSGAERYLTISSLQSEDEADYYCQTWGTGIAVF GGGTQLTPL 50 Anti-PI16 clone 49A7 heavy EVQLLESGGGLVQPGGSLRLSCIASGFTFSSYAM chain variable domain TWVRQVPGRGLEWVSAISGSGFNTYYADSVKGRF TISRDNSKNTLYLQMNSLRVEETALYFCAKDLGM RAQGWFDPWGQGTLVTVSS 51 Anti-PI16 clone 49A7 light QLVLTQSPSASASLGASVKLTRTLSSGLSSYAIA chain variable domain RQQQQPEKGPRYLMKFNSDGSHSKGDGIPDRFSG SRSGTERYVTISSLQSEDEADYYCQTWGTGTAVF GGGTQLTAL 52 Anti-PI16 clone 10E3 heavy EVLLLESGGGLVHPGGSLKLSCAASGFTFSSYAM chain variable domain SWVRQVPGKGLEWVSTISGGGGYTYFADSVKGRF TISRDNSKDTLYLQMNSLRAEDTAVYFCAKDLGS RAQGWFDPWGQGTLVTVSS 53 Anti-PI16 clone 10E3 light QPVLTQPSSHSASSGASVRLTCMLSSGFSVGDFW chain variable domain IRWYQQKPGNPPRYLLYYHSDSNKGQGSGVPSRF SGSNDASANAGILRISGLQPEDEADYYCGTWHSN SKTFIFGSGTKVTVL 54 Anti-PI16 clone 32A4 heavy QVKLVESGGGVVQPGRSLRLSCAASGFTFSSYGM chain variable domain HWVRQAPGKGLEWVAVIWYDGSNKYYIDSVKGRF TISRDNSKNTLYLQMNSLRAEDTAVYNCARDRRI TMVRGVMRGMDVWGQGTTVTVSS 55 Anti-PI16 clone 32A4 light EIVMTQSPATLSLSPGERATLSCRASQSVSSRYL chain variable domain SWYQQKPGQAPRLLIYGASTRATGIPARFSGSGS GTDFTLTISSLQPEDFAVYYCQQDYNLPWTFGQG TKVEIK 56 Human IgG4 HC Constant ASTKGPSVFPLAPCSRSTSESTAALGCLVKDYFP domain (S228P) EPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSV VTVPSSSLGTKTYTCNVDHKPSNTKVDKRVESKY GPPCP

CPAPEFLGGPSVFLEPPKPKDTLMISRT PEVTCVVVDVSQEDPEVQFNWYVDGVEVHNAKTK PREEQFNSTYRVVSVLTVLHQDWLNGKEYKCKVS NKGLPSSIEKTISKAKGQPREPQVYTLPPSQEEM TKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYK TTPPVLDSDGSFFLYSRLTVDKSRWQEGNVFSCS VMHEALHNHYTQKSLSLSLGK 57 Human IgG1 HC Constant ASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFP domain EPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSV (L234A L235A D265S) VTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKS CDKTHTCPPCPAPE

GGPSVFLEPPKPKDTLMI SRTPEVTCVVV

VSHEDPEVKFNWYVDGVEVHNA KTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKC KVSNKALPAPIEKTISKAKGQPREPQVYTLPPSR DELTKNQVSLTCLVKGFYPSDIAVEWESNGQPEN NYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVF SCSVMHEALHNHYTQKSLSLSPGK

The present invention is not to be limited in scope by the specific embodiments described herein. Indeed, the scope of the present invention includes embodiments specifically set forth herein and other embodiments not specifically set forth herein; the embodiments specifically set forth herein are not necessarily intended to be exhaustive. Various modifications of the invention in addition to those described herein will become apparent to those skilled in the art from the foregoing description. Such modifications are intended to fall within the scope of the claims.

Patents, patent applications, publications, product descriptions, and protocols are cited throughout this application, the disclosures of which are incorporated herein by reference in their entireties for all purposes. 

1. (canceled)
 2. An antibody or antigen-binding fragment thereof comprising: (i) a heavy chain variable region comprising CDR1 comprising the amino acid sequence of SEQ ID NO: 10; CDR2 comprising the amino acid sequence of SEQ ID NO: 11; CDR3 comprising the amino acid sequence of SEQ ID NO:12; and a light chain variable region comprising CDR1 comprising the amino acid sequence of SEQ ID NO:13; CDR2 comprising the amino acid sequence of SEQ ID NO:14; CDR3 comprising the amino acid sequence of SEQ ID NO:15; or (ii) a heavy chain variable region comprising CDR1 comprising the amino acid sequence of SEQ ID NO:18; CDR2 comprising the amino acid sequence of SEQ ID NO:19; CDR3 comprising the amino acid sequence of SEQ ID NO:20; and a light chain variable region comprising CDR1 comprising the amino acid sequence of SEQ ID NO:21; CDR2 comprising the amino acid sequence of SEQ ID NO:22; CDR3 comprising the amino acid sequence of SEQ ID NO:23; or (iii) a heavy chain variable region comprising CDR1 comprising the amino acid sequence of SEQ ID NO:26; CDR2 comprising the amino acid sequence of SEQ ID NO:27; CDR3 comprising the amino acid sequence of SEQ ID NO:28; and a light chain variable region comprising CDR1 comprising the amino acid sequence of SEQ ID NO:29; CDR2 comprising the amino acid sequence of SEQ ID NO:30; CDR3 comprising the amino acid sequence of SEQ ID NO:31; or (iv) a heavy chain variable region comprising CDR1 comprising the amino acid sequence of SEQ ID NO:34; CDR2 comprising the amino acid sequence of SEQ ID NO:35; CDR3 comprising the amino acid sequence of SEQ ID NO:36; and a light chain variable region comprising CDR1 comprising the amino acid sequence of SEQ ID NO:37; CDR2 comprising the amino acid sequence of SEQ ID NO:38; CDR3 comprising the amino acid sequence of SEQ ID NO:39.
 3. The antibody or antigen-binding fragment of claim 2 comprising: (i) a heavy chain variable region comprising the amino acid sequence set forth in SEQ ID NO:8 and a light chain variable region comprising the amino acid sequence set forth in SEQ ID NO:9; or (ii) a heavy chain variable region comprising the amino acid sequence set forth in SEQ ID NO:16 and a light chain variable region comprising the amino acid sequence set forth in SEQ ID NO:17; or (iii) a heavy chain variable region comprising the amino acid sequence set forth in SEQ ID NO:24 and a light chain variable region comprising the amino acid sequence set forth in SEQ ID NO:25; or (iv) a heavy chain variable region comprising the amino acid sequence set forth in SEQ ID NO:32 and a light chain variable region comprising the amino acid sequence set forth in SEQ ID NO:33. 4.-8. (canceled)
 9. A complex between ILT3 and ILT3 ligand wherein the ILT3 ligand is PI16.
 10. The complex of claim 9 wherein the ILT3 or ILT3 ligand or both is on the surface of a cell, detectably labeled, bound to a metal surface, bound to an antibody or antigen-binding fragment, or bound to an insoluble substrate. 11-20. (canceled)
 21. A method for determining whether a substance agonizes or antagonizes binding between ILT3 and ILT3 ligand, the method comprising: contacting ILT3 ligand with ILT3 in the presence of the substance and determining whether the ILT3 ligand and the ILT3 form a complex; wherein the substance is determined to agonize said binding if more of the complex is determined in the presence of the substance than in the absence of the substance and wherein the substance is determined to antagonize said binding if less of the complex is determined in the presence of the substance than in the absence of the substance, wherein the ILT3 ligand is PI16.
 22. (canceled)
 23. The method of claim 21, wherein the ILT3 is detectably labeled and wherein the complex is detected by detecting the label bound to the ILT3 ligand; or wherein ILT3 ligand is detectably labeled and wherein the complex is detected by detecting the label bound to the ILT3.
 24. The method of claim 23, wherein the ILT3 is labeled with a FRET (fluorescence resonance energy transfer) acceptor and ILT3 ligand is labeled with a FRET donor; or ILT3 is labeled with a FRET donor and ILT3 ligand is labeled with a FRET acceptor; and wherein the complex is determined to form if FRET between the acceptor and donor is detected.
 25. The method of claim 21, wherein ILT3, which is bound to a gold or silver metal surface on the surface of a glass slide, is contacted with ILT3 ligand and the metal is illuminated through the glass with polarized light wherein, if a change in the refractive index of medium in close vicinity to the metal surface illuminated with the light is detected, then the complex is determined to have formed between ILT3 and the ILT3 ligand; or ILT3 ligand that is bound to a gold or silver metal surface which is on the surface of a glass slide is contacted with ILT3 and the metal is illuminated through the glass with polarized light wherein, if a change in the refractive index of medium in close vicinity to the metal surface illuminated with the light is detected, then the complex is determined to have formed between ILT3 and the ILT3 ligand.
 26. The method of claim 1, wherein the ILT3 ligand is expressed on the surface of a macrophage cell and the ILT3 is fused to a cytosolic domain of CD3 zeta and is expressed on the surface of a T-cell that comprises an NEAT promoter operably linked to a reporter gene and wherein binding is determined if reporter gene expression in the T-cell is detected.
 27. The method of claim 26, wherein the reporter gene is luciferase.
 28. The method of any one of claims 26, wherein the T-cell is a Jurkat cell. 